for smoother upgrade. Update web page.

Apparently, ecl doesn't like (change-class x 'standard-object).

to properly deal with paths gotten with GETENV.
Bug introduced with subpathname in 2.017.27. Should fix debbugs #647544:
http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=647544#10
Thanks to Desmong O. Chang.

and add more extensions to clean in the Makefile.

they break the r-i contract and mess up with asdf-dependency-grovel.

in view of using it in a system-granular parallelizing backend.

Don't defparameter *system-definition-search-functions*, use defvar and fixup.
Clear *systems-being-defined* when upgrading asdf,
but re-find them immediately because they may be needed
as part of a higher operation.
Thanks to Nikodemus for reporting the bug while using quicklisp.

of some internal functions though they may be in the continuation
of an asdf upgrade, because asdf could be loaded by a .asd file
we load while finding a system for a dependency.
Solution: unintern the symbols during an upgrade.

2.018.9: Fix to 2.018.8; since SBCL now cast the same wide net as CMUCL in subdirectories, it needs the same filter.

locating a configuration file for reading vs for writing.
Will hopefully make Xach's life easier.

* split locate-system out of find-system, that tells what find-system would do,
 but doesn't actually cause visible side-effects.
* modify user-configuration-directories and system-configuration-directories
 to return all valid directory names even if the directories do not exist yet,
 so they may be used as the basis for the creation of said directories.

Thanks to p-cos for reporting the bug and a fix.

We should probably refactor some more later... smells like cl-launch...