update: do not pass in user revspec as default destination (issue6044) When the revsingle() was introduced at 61c0df2b089a, it couldn't handle revspec=0 (not '0') properly. That's probably why the default was set to rev. This is technically BC since "hg update ''" was identical to "hg update '.'" whereas "hg update -r ''" is "hg update", but I believe that's a bug given no test fails with this change.