Implement self initializing pretxncommit hook This is more expensive than overriding commit(), but a) uses more "official" interface b) less code c) easier to maintain Get all changes up to cee5fef33cf8 in here as well.

536c1797202d57efb77bea098e10968ff01602ce universal_scheme
ba000e29ecf3b8df09e0fd363a78cabbe3c2a78f cvs_scheme
1fe48bf82d056f1ece05baccab888357c10c5ab8 r0.1