Catch the exception raised with 'hg help <somethingambiguous>'. Example: 'hg help a'

Add revlog.strip to truncate away revisions. This updates the revlog data structures for index and nodemap in place so the .d and .i files don't need to be reread after stripping away a revision.

Optimize manifest.add Testing shows that manifest.add is spending a significant percentage of its time running calcoffsets and doing text = "".join(addlist). This patch removes the need for both of these by storying the manifest in a character array, and using a modified bisect search to find lines without the help of a separate index of line offsets. manifest.add was also reworked to push delta construction/combination into the main loop. Time to apply 2751 patches (without psyco, ext3 noatime,data=writeback): Stock hg: 4m45s real 3m32s user 55s sys patched: 2m48s real 1m53s user 43s sys quilt: 2m30s real 45s user 50s sys (quilt does much more io...)