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
# invalid filenames
test-add.t
test-init.t
test-clone.t
test-contrib.t
test-hgweb-raw.t
test-walk.t
# no sockets or fifos
test-hup.t
# no hardlinks
test-hardlinks.t
test-relink.t
# exec bit problems
test-convert-bzr-114.t
test-convert-bzr-directories.t
test-convert-bzr-merges.t
test-convert-bzr-treeroot.t
test-convert-darcs.t
test-merge-tools.t
# debugstate exec bit false positives
test-dirstate.t
test-filebranch.t
test-merge-remove.t