tests: allow for unstable fortran output ordering.

tests: allow for unstable fortran output ordering.

Due to differences in line-endings between C stdout and Fortran
stdout, as well as unpredictable output ordering between
platforms and runtimes, weaken success criteria to not require
the entire output of fortran programs to match a test case.
* itests/fcdemo.at, tests/f77demo.at (_LT_CHECK_EXECUTE):
Improve comments, and weaken test case to grep for a known line
in the f77 runtime output.

Signed-off-by: Gary V. Vaughan <gary@gnu.org>