Cpstransform_rules: rules after the first irrefutable rule are not compiled

Fixes issue that made compilation segfault: defaultk was called with value (Obj.magic 0)
Cpstransform_rules: rename f to g
Cpsfree: fix comment
OMakefile: add subdirectory cpstransform
Cpstransform: Add files Cpstransform_base and Cpstransform_expression
Cpstransform: Remove Cpstransform_ prefix to Base, Expression, and Rules