cmdutil: split functions of log-like commands to new module (API)
cmdutil.py is painfully big and makes Emacs slow. Let's split log-related
functions.
% wc -l mercurial/cmdutil.py
4027 mercurial/cmdutil.py
% wc -l mercurial/cmdutil.py mercurial/logcmdutil.py
3141 mercurial/cmdutil.py
933 mercurial/logcmdutil.py
4074 total
ERROR: FIXME: This is a known failure of filelog.size for data starting with \1\n
OK.