Set SUBDIRS equal to autoconf variable RTLIBSUBSYS

Otherwise, the make "dist" target fails if Gambit Universal IDE
(guide) is disabled by configure.
Add make "doc" as prerequisite to make "dist" and "dist-devel" targets

Otherwise, make "dist" and make "dist-devel" fails due to missing
documentation deliverables.
lib/mem.c: ___KEY_OBJ -> ___KEYOBJ

___KEY_OBJ was renamed to ___KEYOBJ a little while back, but mem.c
hasn't been updated.
Cosmetic changes to os_io.c
Force commit of lib/_io.c (which is normally commited at new releases) because it must be consistent with lib/os_io.c (which is committed on every commit). The file lib/_io.c contains offsets into the port structure which must be consistent with those defined in lib/os_io.c .

For the record, these commands were used for this special commit instead of a "make commit":

git update-index --no-assume-unchanged lib/_io.c
make stamp
git commit -a
git update-index --assume-unchanged lib/_io.c
The previous forced commit was insufficient to fix the inconsistency problems related to the offsets into the port structure.  Several .c files generated by the Gambit compiler are affected by the changes to lib/_io.scm so the whole set of generated files needs to be committed (not just lib/_io.c).  These commands were used

make select-gen-for-commit
make commit
make deselect-gen-for-commit
To force a commit of the generated files the correct commands are:

make select-gen-for-commit
git commit -a
make deselect-gen-for-commit
Added ##inline-host-code procedure to universal back-end.
Merge pull request #3 from norton/norton-lib-makefile

Set SUBDIRS equal to autoconf variable RTLIBSUBSYS
Merge pull request #4 from norton/norton-makefile

Add make "doc" as prerequisite to make "dist" and "dist-devel" targets
Fixes issue #5
Merge pull request #8 from vyzo/master

Trival: ___KEY_OBJ -> ___KEYOBJ in lib/mem.c