error: introduce StorageError Errors in revlogs are often represented by RevlogError. It's fine for revlogs to raise a revlog-specific exception. But in the context of multiple storage backends, it doesn't make sense to be throwing or catching an exception with "revlog" in its name when revlogs may not even be in play. This commit introduces a new generic StorageError type for representing errors in the storage layer. RevlogError is an instance of this type. Interface documentation and tests referencing RevlogError has been updated to specify StorageError should be used. .. api:: ``error.StorageError`` has been introduced to represent errors in storage. It should be used in place of ``error.RevlogError`` unless the error is known to come from a revlog. Differential Revision: https://phab.mercurial-scm.org/D4654