mq: preserve --git flag when folding patches
Without this, folding a git patch into a regular one downgrades the resulting
patch to a regular patch.
#!/bin/sh
rm -rf a
hg init a
cd a
touch a
hg ci -Am0
hg mv a a1
hg ci -m1
hg co 0
hg mv a a2
hg up
hg ci -m2
touch a
hg ci -Am3
hg mv a b
hg ci -Am4 a
hg ci --debug --traceback -Am5 b
hg verify
hg export --git tip