Code review for LIKE ... INCLUDING INDEXES patch. Fix failure to propagate

Code review for LIKE ... INCLUDING INDEXES patch.  Fix failure to propagate
constraint status of copied indexes (bug #3774), as well as various other
small bugs such as failure to pstrdup when needed.  Allow INCLUDING INDEXES
indexes to be merged with identical declared indexes (perhaps not real useful,
but the code is there and having it not apply to LIKE indexes seems pretty
unorthogonal).  Avoid useless work in generateClonedIndexStmt().  Undo some
poorly chosen API changes, and put a couple of routines in modules that seem
to be better places for them.