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.

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# should print nothing

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# should print ? b/x

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? b/x

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# should print A b/x

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A b/x

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# should forget b/x

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forgetting b/x

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# should print nothing