Emacs support: numerous changes. Most SCM commands now work in derived buffers (e.g. diff viewing buffers) as well as buffers backed by files. diff and log now work properly on repositories and files. Commit support is more solid. Doc strings are better.

removing b
this update spans a branch affecting the following files:
 b
aborting update spanning branches!
(use update -m to merge across branches or -C to lose changes)