rebase: abort in-mem rebase if there's a dirty merge state
In-memory merge uses the on-disk merge state, so we should not allow
it run in-memory merge when the merge state is not clean. We should
probably not use the on-disk merge state when running in-memory merge,
but chaning that is not suitable for the stable branch.
Differential Revision: https://phab.mercurial-scm.org/D5357
$ hg init
$ touch a
$ unset HGUSER
$ echo "[ui]" >> .hg/hgrc
$ echo "username= foo" >> .hg/hgrc
$ echo " bar1" >> .hg/hgrc
$ hg ci -Am m
adding a
abort: username 'foo\nbar1' contains a newline
[255]
$ rm .hg/hgrc
$ HGUSER=`(echo foo; echo bar2)` hg ci -Am m
adding a
abort: username 'foo\nbar2' contains a newline
[255]
$ hg ci -Am m -u "`(echo foo; echo bar3)`"
adding a
transaction abort!
rollback completed
abort: username 'foo\nbar3' contains a newline!
[255]