Use MAPI/SPLICE instead of MERGE
Define and use MAP/PAIRWISE instead of MAP2
Don't do diff-based checking for cross-compilation

With t-exprs, the order of some outputted statements may change
because of iteration over table keys. The new pattern for checking
cross-compilation correctness is `make cross test'.
Fix a cross-compilation bug in TERMINATOR
Get rid of MAPK and generalized MAP

It didn't turn out to be as useful as anticipated.