* lib/am/depend2.am (%SOURCEFLAG%): New substitution, goes

* lib/am/depend2.am (%SOURCEFLAG%): New substitution, goes
right before the expanded source file name.
* automake.in (%sourceflags): New global: per-extension flag
to denote that the next compiler argument is the source file.
(scan_autoconf_traces): Trace AC_FC_SRCEXT; initialize
%sourceflags accordingly.
(handle_single_transform): Store source file extension in...
(%lang_specific_files): ...this and...
(handle_languages): ...adjust here.  Pass flag in SOURCEFLAG.
* doc/automake.texi (Optional): Add AC_FC_SRCEXT.
(Fortran 9x Support): Update.
* tests/fort2.test: New test.
* tests/Makefile.am: Adjust.
* NEWS, THANKS: Update.
Suggested by Steven G. Johnson.