Output pair kerning according to sf->preferred_kerning.
Support sf->preferred_kerning in S. F. D..
Allow for over-riding this value in the Generate Fonts dialogue.
Map all kerns from U. F. O. native files (which lack script designators) to the DFLT script.
Add disabled code for guessing scripts.

Add a macro for enabling script guessing for U. F. O. import.

ufo: unbork a loop in UFOOutputGroups()

Fix a logic error.

Fix another logic error.

Set the script to the default before populating the kerning class table when importing from U. F. O..
Fix U. F. O. name numbering.

Fix a problem with U. F. O. kerning class naming.
Fix old memory corruption that may be causing irregular problems with U. F. O. kerning output.
Fix a crash that occurs in the kerning class dialogue when deleting a class that never existed.
Merge pull request #1950 from fontforge/ufo_class_kerning_script_detection_3

Enhance class kerning support.