Generate simple case folding tables only if asked

Generate simple case folding tables only if asked

Speed up mktables by not generating the simple case folding tables
unless asked to.  Previously the simple tables were generated, and then
the full tables were initialized with them, and then overwritten with
the full mappings.  This is an artifact from the fact that the data
comes to us in two files, one  with the simple mappings (among other
things), and another with the full mapping overrides.  Now, the full
tables are initialized from the first file, and the second file
overrides the full mappings.  The simple tables are not generated by
default, so this saves, copying them.