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
# a test for issue586
hg init a
cd a
echo a > a
hg ci -Ama
hg init ../b
cd ../b
echo b > b
hg ci -Amb
hg pull -f ../a
hg merge
hg rm -f a
hg ci -Amc
hg st -A