submodule handling

Replying to anonymous:

the code breaks at some places in git_fs, on commits having submodule changes. the first one i found is get_content_length returning None, and then trac trying to sum Nones. a quick workaround is changing {{{ if not self.isfile: return None }}} to {{{ if not self.isfile: return 0 }}} the second is in get_changes. submodule changes have a different mode than directory changes, so they end up with kind = file, and trac tries to read the content. my workaround is changing the condition {{{ if mode2.startswith('04') or mode1.startswith('04'): kind = Node.DIRECTORY }}} to {{{ if mode2.startswith('04') or mode1.startswith('04') or mode1.startswith('16'): kind = Node.DIRECTORY }}} so these changes are treated like directory changes. these are just some quick hacks, but they make the plugin usable on repos with submodules, until there's a better solution.

see also #3104