Some doc & test frobbing.

Rename RUN-PROGRAM/ to RUN-PROGRAM.
Can't export it from ASDF because it causes a clash in SB-GROVEL.

Rename SUB-OBJECT and :PATH to ACCESS-AT and :AT.

Get rid of TRANSLATE-OUTPUT-P.
Instead, check whether the component's BUILD-OPERATION
is the same as the current operation.

* Pathname support has been cleaned up, yet again,
 extending and renaming COERCE-PATHNAME into PARSE-UNIX-NAMESTRING,
 also ENSURE-PATHNAME, many docstrings, and plenty of small enhancements.
* Bundles were refactored to take advantage of the new, more sensible,
 component-depends-on semantics.
* Image support was cleaned up again, and program-op was implemented
 to produce a standalone executable on supported platforms;
 a working hello-world-example is included amongst tests.
* The *compile-file-function* indirection was removed, with the
 ECL and MKCL object file support
 being folded into compile-file* instead.
* systems now can have NIL as component-pathname,
 instead of providing a non-sensible bogus pathname
 when no sensible pathname was determined.
 Most of our pathname functions have sensible default behavior
 when provided NIL instead of a pathname as an argument.

Should make fe[nl]ix happy.

Much cleanup in image support and hooks.
More package hacking.
New feature for :version: `(:read-file-from ,path) - thanks to Stelian Ionescu.
The driver now homesteads the package nickname d.
Rename-package it away if you don't like it.

This assumption is notably made by tens of systems that use
the old ASDF1 method of specifying the pathname type for components:
(defmethod source-file-type ((c foo-file) (s module)) "foo")
Sigh. My bad for recommending people use module and not system, here.

Document that weakly-depends-on is deprecated.

Or else force-not :all won't be as useful.

where it ought to always have been, based on a properly cleaned up prepare-op
(previously introduced in 2.26.14 as parent-load-op).

This is a checkpoint of a mostly working system after major changes;
it requires further cleanup and fixes:
strangely, fails some tests on CCL but not SBCL.

Introduce find-operation as a companion to find-component,
subsuming make-sub-operation.
The results of component-depends-on are processed with find-operation and resolve-component-spec.
component-self-dependencies is fixed to play well with prepare-op.

Also, some internal renamings and signature changes:
parent-operation becomes upward-operation
parent-load-op becomes prepare-op
parent-source-load op becomes prepare-source-op
parent-component is distinguished from module
module-components becomes component-children
module-components-by-name becomes component-children-by-name
compute-module-components-by-name becomes compute-children-by-name
circular-dependency-components becomes circular-dependency-actions
component-load-dependencies becomes component-sibling-dependencies (with a stub)
introducing child-component, downward-operation.
refactoring visit-dependencies to include the loop in which it's always used.
refactoring force and force-not processing to use a function action-override-p;
force is achieved with a trivial method on operation-done-p for prepare-op,
and force-not as a trivial check in visit-action.

Tweak tests along the way. Tweak the documentation.

Failed to either rename operation-error or introduce action-error in its superclasses:
that breaks sb-grovel.

Also fix some texinfo syntax.

This allows for consistency check of .fasl output before the file can possibly be seen
by other builds (i.e. no race condition).

Notably specify the inheritance behaviour of :encoding.

Update documentation somewhat.

This ensures backwards compatibility with 2.20 and earlier,
for now, until the dust settles on asdf encodings.
Update documentation about encodings.
Export more utilities. Document some of them.
Remove ununspecific. Accept :unspecific on more implementations.

Minimal documentation.

WEAKLY-DEPENDS-ON needed to pass the ERROR-P NIL to FIND-SYSTEM in order
to behave properly.

Added documentation for previously-undocumented weakly-depends-on.

Major change for RMCL: location strings are now POSIX namestrings.
Major change for logical pathnames: they are now preserved by source-registry;
the price is that only logical pathnames for which merging the name and type
commutes with truename will be found by directory-files and subdirectories.
Minor change for GCL: dropped kluges for 2.6, which never was working.
Simplifications in internals of (implementation-identifier).
Removed *system-cache* and get-uid, which never were working right
(bad attempts at allowing common-lisp-controller compatibility,
but it only ever was but a giant gaping security hole in the waiting).
Simplified resolve-relative-location-component
(ugly because it was written before MERGE-PATHNAMES*).
Updated documentation about the file location DSL.

Add doc compilation to release tests!