Fortran Cray pointer macro support

Fortran Cray pointer macro support

This patch adds the AC_F77_CRAY_POINTERS and AC_FC_CRAY_POINTERS macros,
which test if the Fortran compiler supports Cray pointers.

The macros are written such that the tests share a common backend
(_AC_FC_CRAY_POINTERS) which works on both F77 and FC compilers.
Wrappers are provided to address any future potential compatibility
issues.

The macros include additional tests for particular flags required by
GFortran and PGI compilers.  The current set of flags is sparse, but can
be extended for other compilers if needed.

Documentation and a minimal test of the macro have been included.

Two minor variable name typos (@EXEEXT@ as @EEXEXT@) were also fixed in
two of the other Fortran tests.