[PATCH 0 of 2] make graphlog behaviour similar to log

[Vishakh]

glog always displays the graph by decreasing revisions
'hg glog -r tip:0' == 'hg glog -r 0:tip'
this is unlike log which does the right thing.
these patches ensure that glog moves in the right direction 
depending on the revision range. 
the changes to graphlog.py allow it draw graphs either ways.
continuing in this direction includes brining glog behavious more
inline with that of log, including situations like:

    *making 'glog -r 0:tip[FILE]' behave correctly [not dealt with
     in this patch]

    *'hg log -r a:b FILE' will not display any results when
     there are no changesets modifying FILE in [a,b] , but
     glog will display the highest changeset not greater than a or b