Teach walk code about absolute paths. The first consequence of this is that absolute and relative paths now all work in the same way. The second is that paths that lie outside the repository now cause an error to be reported, instead of something arbitrary and expensive being done. Internally, all of the serious work is in the util package. The new canonpath function takes an arbitrary path and either returns a canonical path or raises an error. Because it needs to know where the repository root is, it must be fed a repository or dirstate object, which has given commands.matchpats and friends a new parameter to pass along. The util.matcher function uses this to canonicalise globs and relative path names. Meanwhile, I've moved the Abort exception from commands to util, and killed off the redundant util.CommandError exception.