Log Message:
libgsf: updated to 1.14.50

libgsf 1.14.50
* Fix error handling problem when writing ole files.

libgsf 1.14.49
* Use g_date_time_new_from_iso8601 and g_date_time_format_iso8601
  when available.  See merge request 9.
* Fix problems with non-western text in OLE properties.

libgsf 1.14.48
* Fix win32 build.
* Add "zip64" readable property of GsfInfileZip.