Change the way libguile and boot-9.scm are timestamped, to try to

Change the way libguile and boot-9.scm are timestamped, to try to
get rid of these spurious mismatch warnings.  Now both
libguile/versiondat.h and ice-9/version.scm are generated directly
by the configuration process, rather than having version.scm
generated directly, and libguile/versiondat.h generated by the
Makefile, which is generated by configure.  It seems that
sometimes the Makefile would change, but versiondat.h depends on
Makefile.in, not Makefile, so it wouldn't get rebuilt.
* Makefile.am (versiondat.h): Target removed; this is generated
directly by the configure script now.
(BUILT_SOURCES): Remove versiondat.h.
* versiondat.h.in: New file, transformed by the configure script
into versiondat.h.
* Makefile.in: Regenerated.