contrib: add "hgperf" command to measure performance of commands easily
Newly added "hgperf" command repeats "dispatch.runcommand()" for
specified Mercurial command and measure performance of it in the same
manner of "contrib/perf.py" extension.
Users (mainly developers) can examine performance of the target
command easily, without adding new entry for it to "contrib/perf.py"
extension.
http://example.com/no/anchor, branches: (None, [])
http://example.com/an/anchor, branches: ('foo', [])
http://example.com/no/anchor/branches, branches: (None, ['foo'])
http://example.com/an/anchor/branches, branches: ('bar', ['foo'])
http://example.com/an/anchor/branches-None, branches: ('foo', [])
http://example.com/, branches: (None, [])
http://example.com/, branches: (None, [])
http://example.com/, branches: ('foo', [])