Fix a few glaring recent bugs.

Update documentation.
Fix implicit build (default without --build).

+ Partial changes to get xcvb to build a binary of xcvb.
+ Extending :create-image to support executables.
+ Support for command line arguments when resuming the executable.
  These are passed to the entry-point. However, each lisp vendor
  mangles the argv a little and it needs work to be really right.
  For now it is good enough.
+ dump-image for ecl got hacked upon, but it is currently broken.
+ Changed example-1 to produce an executable, but currently this
  only works for lisp implementations which can produce them. This
  needs more consideration in the future, for example, the
  "executable" could be a script which invokes an image.
+ simple-build can now accept targets with empty computations.
  This implements the "phony target" idea in simple-build.

My, that what much more painful than it ought to be.

* fix various bugs left over from .507.
* back out generation of Lisp files in object tree
 until we can provide build processes with a mapping from name to pathname.
* pass self-test.

Some documentation update.
Tweak hello Makefile for ASDF 2.
re-Hush warning from registry.
Add require-asdf.

This release doesn't work at all.

* Rename handle-lisp-dependencies to finalize-grain. Refactor generators.
* Commented out stuff in cffi-grovel-support, virtual-pathnames.
* Some INTERNALS update

change SBCL_HOME unsetting to be less uniform but more portable.
Fix posix-wait in CLISP as in the recent POIU fix.
My, we need a regression test suite!

* Introduce the world-grain abstraction as a step towards a farmer.
* A few important cleanups and refactorings.
* better hush the build

* allow lisp modules with their own build-dependencies different from their parent.

Documentation update.

Complete the non-enforcing makefile backend.
Refactor a bit the asdf backend along the way.
Debug portablish-pathname, main.

Had to do a few things by hand to compile xcvb itself with poiu:
   mkdir obj-ne ; ln -s ../../poiu/poiu.asd obj-ne/ ;
   xcvb nm --build xcvb --parallel && make -f xcvb-ne.mk

Nothing functional yet, but checkpointing my work.
More documentation update.