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.
repoview: update documentation of _getstatichidden
In 2f7cb6e6acdd, the function name, role and return was changed. But the
documentation was not. This fixes it.