rhg: support status --change, including --copies...
rhg: support status --change, including --copies
It works by parsing copy information from filelog metadata headers. The
--rev --rev --copies case still falls back to Python since that will
require constructing a map like pathcopies does in copies.py.
As in Python, rhg by default only reports copies for newly added files. With
devel.copy-tracing.trace-all-files=True, it also does it for modified files.
