patch.diff: avoid calling workingctx().manifest()
Right now, to generate the manifest of the working dir, we have to
perform a full walk of the working dir, which will be very slow,
especially if we're interested in only a small part of it.
Since we use the manifest only to find out the mode of files for git
patches, manually build an execf function to do it.
This should fix issue567.
#!/bin/sh
hg init
echo "Is there an error message when trying to diff non-existing files?"
hg diff not found
echo "Is there an error message when trying to add non-existing files?"
hg add not found