Define a toString for PatchListKey to improve errors

If we can't format a diff, Ehcache dumps the PatchListKey's toString
into part of the exception text.  Instead of outputting the useless
Java object identity hash code, display the Git commit(s) involved,
and the project they are expected to appear in.

Change-Id: I7eef60bfe6c9703d345650286cac4031a6ced930
Signed-off-by: Shawn O. Pearce <sop@google.com>
1 file changed