Functionality to print a dependency list for a Fortran code base

[dorchard]

Provides the --show-make-list option to print dependency list from tree to root, e.g.,

% fortran-src --show-make-list test-data/module/.
test-data/module/./leaf.f90
test-data/module/./mid1.f90
test-data/module/./mid2.f90
test-data/module/./top.f90

(where top uses mid1 and mid2 and both of these use leaf). This PR includes a test for this with some fixture data and makes a small improvement to error reporting for --show-make-graph).

[dorchard]

Requested by @jaytorry.

[dorchard]

Updated to remove duplicates due to unusual non-standard import patterns.

[dorchard]

@jaytorry - are you happy with this functionality now? If so I will merge it.

[jaytorry]

@dorchard - Yes seems to be working well now.