Avoid warnings about conftest.dSYM directories on Mac OS X Leopard.

Avoid warnings about conftest.dSYM directories on Mac OS X Leopard.

* lib/autoconf/general.m4 (_AC_LINK_IFELSE, _AC_RUN_IFELSE):
Remove conftest.dSYM directory.
* lib/autoconf/fortran.m4 (_AC_PROG_FC_V_OUTPUT)
(_AC_LANG_PROGRAM_C_, _AC_FC_MAIN, __AC_FC_NAME_MANGLING):
Remove `conftest.*' recursively.
* lib/autoconf/lang.m4 (AC_LINK_IFELSE): Likewise.
* lib/autoconf/specific.m4 (_AC_SYS_LARGEFILE_MACRO_VALUE):
Likewise.
(_AC_COMPILER_OBJEXT_REJECT): Reject *.dSYM.
* THANKS: Update.
Report and analysis by Jeff Squyres and Peter O'Gorman.