Sources should discover module source files called with 'load'

[dannypurcell]

Currently Rubycom's Sources module only finds source files for sub-modules when those files were loaded with a call to 'require'.
Sources should also be able to locate the files when loaded by a call to 'load'.

This is probably just a matter of making Sources.module_source search the $LOAD_PATH in addition to $LOADED_FEATURES.