[svn-r6940] Replaced enable_fc=default setting by enable_fc=yes and set enable_fc=no if any Fortran90 test fails.  Guarded all AC_PROG_[CC|F77|FC|CXX] so none of the *FLAGS would be set -g -O2.  Eliminated duplicated PAC_PROG_FC/PAC_PROG_FC_WORKS caused by inconsistent use of enable_fc=default.  Moved AC_PROG_[CC|F77|FC|CXX] right before the corresponding language tests to improve readability of the code.

[svn-r6852] Initial deposit that removes the AC_LANG=[Fortran 90] and replaces it by AC_LANG=[Fortran] which is officially supported by autoconf.  The replaced PAC macros in aclocal_fc.m4 is also rewritten by replacing all use of AC_TRY_* by AC_*_IFELSE style as recommented by autoconf.  The change also removes some old autoconf macros date back to at least 2.13 as in aclocal_cross.m4.  The change that users see is to use FC/FCFLAGS instead of F90/F90FLAGS which will no longer be supported.  This also includes some misc fixes that allow mpif90 to access mpi.mod during build process....

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