1.9.4:

* SourceBuffer: Added *_source_mark() methods.
* Added SourceMark.
* Added SourceStyleSchemeManager.
  (Jonathon Jongsma)
* SourceBuffer, SourceMark, SourceView:
  Some const corrections and refcounting corrections.
  (Murray Cumming)
* Correct the installation of the .m4 gmmproc files.
  (Yselkowitz)