When opening SCM manager folder TM opens untitled document in the editor area and the target folder in file browser. When one sets `windowTitle` to display SCM branch this is not displayed for untitled document. So one needs to open some existing file first.
This change sets SCM variables also for untitled document as if it was saved in selected file browser folder, effectively showing current SCM branch.
There is a minor functional change in that the custom callback type uses event loop signaling that makes it safe to trigger the callback from a thread. This should however not be necessary for timers (which are all setup on the main thread).
This happens e.g. if we do ‘ls|mate’ — here we do have content which got a charset and newline mode assigned during “load”, but from the user’s POV he is saving a new file (if he saves the buffer) so should get his configured encoding.
There is also a new document_t::encoding_for_save_as_path which returns the encoding that would be used for the document, if saved at the given path. If the document was loaded from disk, it will return the encoding used during load, otherwise it will check tmProperties for which encoding should be used for the path provided. Save dialog for untitled documents will be pre-populated with the result of the above function.
