verify: allow suppressing warnings about extra files The verifier issues warnings when the set of files in .hg/store doesn't align with the set of files that are advertised via repo.file(f).files() for all files seen in ctx.files() changelog traversal. This logic is reasonable for a default implementation. But some stores may have extra files whose presence is harmless. Or those stores may not have the same transaction rollback semantics that unlink files as other stores. This commit adds support for disabling the warning for orphaned files. The simple store extension has been taught to set this flag. Differential Revision: https://phab.mercurial-scm.org/D3097