src/: Add compile_error() and compiler_warning() variants which
take a filename and line number, or a prefix to get the filename
and line number from.
lib/survex.pot,src/commands.c,tests/cavern.tst,
tests/omitfixaroundsolve.out,tests/omitfixaroundsolve.svx: If there's
more than one *fix command with coordinates, the station name of the
previous one, plus the file and line number where it was.