Bug 634763 - Fortran: external subroutine as dummy argument not recognized

Besides as as attribute the external can also be used as "type"
Previous commit (pull request 121) was reverted (pull request 122) due to warning message.
Merge pull request #224 from albert-github/feature/bug_634763_2

Bug 634763 - Fortran: external subroutine as dummy argument not recognized