manifest: use rev() instead of nodemap.__contains__ nodemap is an implementation detail of revlogs and isn't appropriate to expose on the manifest storage API. While revlogs don't have a __contains__, they do have lookup() for resolving a value to a node. And this calls rev(), whose API is documented to raise LookupError if a node doesn't exist. And the parameters to LookupError are identical to what was being raised here. So this change should be backwards compatible. Differential Revision: https://phab.mercurial-scm.org/D4279