Multiple program units in one source file

It is valid for Fortran source files to contain multiple program units. This is certainly done by the pFUnit processing script which generates source files with both program and module in them.

We should check that Fab can cope with this.

Start by tracing how Fab processes Fortran source files and compare that with the pFUnit-generated files containing both a program and a module. Reproduce the case with a source file containing multiple program units, then verify that Fab processes it successfully without dropping or misidentifying a unit.

Written by the indexing model from the issue text.