Update coverage.py
There is no technical reason to update it except it contains all the patches
already done in mercurial plus other stuff. It will be easier to update and
maintain in the future.
Escape '%' when writing to hgrc (
issue1199)
Fixes clone with paths containing '%'.
Patch provided by mjc.
tests: fix reported patch tool name in test-mq
Strip any path of the patch executable, which it might return on failure.