context: drop support for changeid='' (API)...
context: drop support for changeid='' (API)
Since the previous commit, there seem to be no users who pass '' to
repo.__getitem__, so let's drop support for it.
It may seem like a small cost to keep support for it, but I've spent
time being confused by it twice already.
Differential Revision:
https://phab.mercurial-scm.org/D3021
