revlog: compute correct deltaparent in the deltaparent function It now returns nullrev for chain base revisions, since they are conceptually deltas against nullrev. The revdiff function was updated accordingly.

changelog: fixes leaked file handle

setdiscovery: limit lines to 80 characters

subrepo: use code from 71ea5b2b9517 only if Python needs it (issue2795) With Python >= 2.6 the original code already works correct, therefore the fix for issue2556 on Python <= 2.5 broke relative subrepositories with newer versions of Python.