Improved date support

[Matt Mackall]

The date handling support in tip has been greatly improved. Commands
that take dates can now handle things like:

  Dec 12       (this year)
  3:30pm       (today)
  5/1/99       (May 1 1999)
  1999-5-1     (same)

The log, update, and revert commands now accept a date option. For
log, this specifies a date range like so:

  <Dec 12      (before December 12th, inclusive)
  >3:30pm      (after 15:30 local time)
  May 5 to Jun 2
  2005         (only changes in 2005)
  -5           (in the last five days)
  Dec 8        (everything on December 8th)

For update and revert, the date option specifies the tipmost revision
matching that date, like so:

  $ hg co -d "Aug 2005"
  Found revision 1182 from Wed Aug 31 21:07:36 2005 +0200

Also, you can now type "hg help dates" to get help on date formats.

-- 
Mathematics is the supreme nostalgia of our time.