Bug 625601 - FORTRAN: recognition free versus fixed formatted code

The recognition of the type (free or fixed) of Fortran code is not reliable possible. A well known possibility as used with compilers as well is to specify the type of code by means of the extension.
With EXTENSION_MAPPING it is possible to select the type of Fortran code, when not explicitly set doxygen tries to guess the type of Fortran code.