hgext/convert/cvs.py can be confused by certain log entries.

The most recent example I ran into was a log entry that had 28 dashes in the
middle of the log.  This confused cvs.py which expected a revision line to
be next.

 .
 .
----------------------------
revision 1.6.10.3
date: 2009/05/22 22:07:49;  author: foo;  state: Exp;  lines: +9 -1
branches:  1.6.10.3.4;
merge from head:
   ... blah blah
----------------------------
date: 2009/04/19 15:48:16;  author: mtm;  state: Exp;  lines: +4 -2
  ... blah blah some change on head
----------------------------
 .
 .

This is only one cvs log entry, but cvs.py gets confused and thinks
otherwise, throwing this error:

AssertionError: expected revision number

Possible solutions?
 - don't die on unexpected log parsing issues, but rather assume it was not
a new cvs log entry
 - better: use cvs to grab the log entry instead of trying to guess where
log entries begin and end in cvs.py (e.g., 'cvs log -N -r1.6.10.3' in the
above example would output the log lines which we can record and skip over
in cvs.py)