Merged updated gtk library.
GTK wrapper only disconnects handlers when marked to destroy contained widgets.
Got expand working, converted to the new gtk, fixed some small bugs.
Moved out-of-bounds line drawing check from rundata to image so that we also avoid adding invalid lines to undo data.
Added percent based brush sizes (percent of smallest dimension).  Reinstated 50 undo levels to prevent (some) crashes from excessive memory usage.  Made quit unsaved changes warning more paranoid.
Standardized little endian saving appears to be working.  Added new file format that might be fluid until next release.
Fixed submodule paths.
Fixed file loading versioning.  Fixed legacy loading to use old-style runs, it should be working fine now.  Old style loading doesn't check for native int size or endianness, it just uses the native formats.