repoview: directly skip public head in _getstatichidden Public heads have nothing to offer regarding hidden stuff, let's skip them.

repoview: simplify process in _getstatichidden Since all children are processed before their parents, we can apply the following algorithm: For each rev (descending order): * If I'm still hidden, no children will block me, * If I'm not hidden, I must remove my parent from the hidden set, This allows us to dynamically change the set of 'hidden' revisions, dropping the need for the 'actuallyhidden' dictionary and the 'blocked' boolean in the queue. As before, we start iterating from all heads and stop at the first public changesets. This ensures the hidden computation is 'O(not public())' instead of 'O(len(min(not public()):))'.

repoview: use a heap in _getstatichidden Since we want to process all non-public changesets from top to bottom, a heap seems more appropriate. This will ensure any revision is processed after all its children, opening the way to code simplification.