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.
pulling from ../a
searching for changes
abort: repository is unrelated
pulling from ../a
searching for changes
warning: repository is unrelated
adding changesets
adding manifests
adding file changes
added 1 changesets with 1 changes to 1 files (+1 heads)
(run 'hg heads' to see heads, 'hg merge' to merge)
changeset: 1:bdcee5d51fa6
tag: tip
parent: -1:000000000000
user: a
date: Mon Jan 12 13:46:40 1970 +0000
summary: a
changeset: 0:f155ba1aa5ba
user: b
date: Mon Jan 12 13:46:40 1970 +0000
summary: b