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

revsetlang: add utility function to return hash like symbols from the tree Functionalities like unhiding changesets whose rev/hash is passed by the user required the knowledge of rev/hashes in the user provided specs. This patch adds functions which can parse tree object and return a list of such values. Differential Revision: https://phab.mercurial-scm.org/D1732