This is still not correct; if an absolute non-existent path is
supplied to "darcs changes", it should not print any patches.
Currently it prints *all* patches.

$ with-temp-dir
with-temp-dir: entering directory `/tmp/with-temp-dir.MrgYvV'
This directory will be deleted when you exit.
$ darcs init
$ touch x
$ darcs rec -lam x x
Recording changes in "x":

Finished recording patch 'x'
$ darcs changes y
Changes to y:

$ darcs changes /y
Ignoring non-repository paths: /y
Thu Mar 19 22:12:20 EST 2009  Trent W. Buck <trentbuck@gmail.com>
  * x
$ darcs --version
2.2.0 (release)
$

This is a very minor bug, but there should be a general solution.  The problem
is that darcs filters out paths which are invalid.  What it should probably do
is to have a special little bit of intelligence for when the only paths given
are invalid.