ui: add I/O descriptors

import: add --bypass option This feature is more a way to test patching without a working directory than something people asked about. Adding a --rev option to specify the parent patch revision would make it a little more useful. What this change introduces is patch.repobackend class which let patches be applied against repository revisions. The caller must supply a filestore object to receive patched content, which can be turned into a memctx with patch.makememctx() helper.

import: separate parents selection from working dir update This will be useful when patching without updating the dirstate

patch: extend filtestore to store an optional copy source This will help wrapping filestores in memctx.

paper/coal: use fixed width for diffstat +/- link The plus and minus characters are normally not the same width in a non-monospace font, and this made the line length change when the diffstat display was toggled. The square brackets are not rendered in a monospace font to ensure that they align with the parenthesis on the same line.

hg: rename opts argument to peeropts in clone This should make it clearer that the options are used with remoteui only and are not used otherwise in hg.clone.

hg: move peerschemes back to schemes This will avoid breaking things with extensions until peers are fully separated from repos.