vc-log bug?

[Giorgos Keramidas]

Some of the recent VC changes broke vc-log for Mercurial here.  My HOME
directory now has less than 2000 changesets:

  changeset:   789:943233c01bf5
  tag:         tip
  user:        Giorgos Keramidas <address@hidden>
  date:        Mon Dec 14 08:49:03 2009 +0200
  summary:     agenda: update clock/time table for today's work

but when I type `C-x v l' the latest VC code tries to see the log of
changes 2000:tip.  Since there is no revision numbered 2000 vc stops
with a backtrace of:

: Debugger entered--Lisp error: (error "Running hg log -r2000:
: AGENDA...FAILED (status 255)")
:   signal(error ("Running hg log -r2000: AGENDA...FAILED (status 255)"))
:   error("Running %s...FAILED (%s)" "hg log -r2000: AGENDA" "status 255")
:   vc-do-command("*vc-change-log*" 0 "hg" ("/home/keramida/AGENDA") "log"  
"-r2000:")
:   apply(vc-do-command "*vc-change-log*" 0 "hg" ("/home/keramida/AGENDA") 
("log" "-r2000:"))
:   vc-hg-command("*vc-change-log*" 0 ("/home/keramida/AGENDA") "log" "-r2000:")
:   apply(vc-hg-command "*vc-change-log*" 0 ("/home/keramida/AGENDA") "log" 
"-r2000:")
:   vc-hg-print-log(("/home/keramida/AGENDA") "*vc-change-log*" nil nil 2000)
:   apply(vc-hg-print-log (("/home/keramida/AGENDA") "*vc-change-log*" nil nil 
2000))
:   vc-call-backend(Hg print-log ("/home/keramida/AGENDA") "*vc-change-log*" 
nil nil 2000)
:   vc-print-log-internal(Hg ("/home/keramida/AGENDA") "789" nil 2000)
:   vc-print-log(nil 2000)
:   call-interactively(vc-print-log nil nil)

Is there any way to tweak the limit automatically to, say, half of the
revisions in the current repository?