SourceParser should only sort file list on globs

[lsegal]

When the SourceParser class currently parses a list of files it does so by sorting the list by path length, guaranteeing that "lib/foo.rb" is parsed before "lib/foo/bar.rb" (which might rely on the "parent" file). However, because the parser sorts all files, it is currently not possible to manually override this sorting order. For instance, it should be possible to do the following:

$ yard doc lib/foo/bar.rb lib/**/*.rb

The above should parse "lib/foo/bar.rb" before "lib/foo.rb". This does not currently work. The solution is to only perform sorting on globs, and assume that single files are listed in the exact order which they are presented.