The top of an index equality loop normally starts with OP_SeekGE and OP_IdxGT.

The top of an index equality loop normally starts with OP_SeekGE and OP_IdxGT.
This check-in adds a flag to OP_SeekGE such that it fails immediately if
the key is not equal, then jumps over the OP_IdxGT, saving a call to the key
comparison functions.  Consider this check-in a proof-of-concept.  It needs
improvement before going on trunk.  Some tests fail, but only because they
new use fewer key comparisons than expected (which is a good thing!).

FossilOrigin-Name: 32e31b9bc8664afcd326a1ff3892d86dc5202474