repoview: add a new filtername for accessing hidden commits

This patch adds a new filter 'visible-hidden' for repository and will be used to
return a repo object with user passed revisions unhidden. Unlike the
directaccess extension in fb-hgext and previous series adding the functionality,
this time we introduce only one new filter as whether to warn user or not is
handled by scmutil.unhidehashlikerevs().

Differential Revision: https://phab.mercurial-scm.org/D1734

mercurial/branchmap.py

@@ -84,6 +84,7 b' def read(repo):'
 # This create and ordering used for branchmap purpose.
 # the ordering may be partial
 subsettable = {None: 'visible',
+               'visible-hidden': 'visible',
                'visible': 'served',
                'served': 'immutable',
                'immutable': 'base'}

mercurial/repoview.py

@@ -143,6 +143,7 b' def computeimpactable(repo, visibilityex'
 # Otherwise your filter will have to recompute all its branches cache
 # from scratch (very slow).
 filtertable = {'visible': computehidden,
+               'visible-hidden': computehidden,
                'served': computeunserved,
                'immutable':  computemutable,
                'base':  computeimpactable}