Does not take an "=" as part of the name of a source file.

pgi, unlike our other compilers, will not accept an "=" as part of a source file name.

Even worse, it gives a very cryptic error message:

> ftn a=b.f
/opt/cray/xt-asyncpe/3.8/bin/ftn: INFO: linux target is being used
/opt/pgi/10.3.0/linux86-64/10.3/lib/f90main.o: In function `main':
f90main.c:(.text+0x3c): undefined reference to `MAIN_'

> cat a=b.f
      program a=b
      print *,"this shows a problem with pgi"
      end