When merging the variable_set_lists for two targets it could be
that the "from" set list is a subset of the "to" set list: check
for this situation to avoid freeing used memory.
* src/variable.c (merge_variable_set_lists): Walk the "to" list and
if the "from" list is contained in it, nothing to do.
* tests/scripts/features/se_explicit: Add a test.
Move the source code (other than glob) into the "src" subdirectory.
Update all scripting and recommendations to support this change.
* *.c, *.h, w32/*: Move to src/
* configure.ac, Makefile.am, maintMakefile: Locate new source files.
* Basic.mk.template, mk/*: Update for new source file locations.
* NEWS, README.DOS.template: Update for new locations.
* build.template, build_w32.bat, builddos.bat: Ditto.
* po/POTFILES.in: Ditto
* tests/run_make_tests.pl, tests/scripts/features/load*: Ditto.
* make.1: Move to doc.
* mk/VMS.mk: Add support for building on VMS (hopefully).
* makefile.vms, prepare_w32.bat: Remove.
* SCOPTIONS: Update to define HAVE_CONFIG_H