document_find_by_filename().
Make document_find_by_filename() take only a utf8_filename argument,
and now match any documents that have a filename set but aren't saved
on disk.
Add document_find_by_realpath() to the plugin API.
Add filename argument for document_save_file_as().
Add GeanyDocument::real_path field, which if non-NULL indicates the
file once existed on disk (not just as an unsaved document filename).


git-svn-id: https://geany.svn.sourceforge.net/svnroot/geany/trunk@2637 ea778897-0a13-0410-b9d1-a72fbfd435f5