mq: really remove undo after a qpush (and after a strip)
For qpush, removeundo has to be called after the transaction has finished.
strip may use unbundle, which also leaves an undo file.
Fixes
issue780.
#!/bin/sh
mkdir t
cd t
hg init
echo a > a
hg add a
hg commit -m "test" -d "1000000 0"
hg verify
hg parents
hg status
hg rollback
hg verify
hg parents
hg status