histedit: add histedit state class Add an histeditstate class that is intended to hold the current state. This allows us encapsulate the state and avoids passing around a tuple which is based on the serialization format. In particular this will give actions more control over the state and allow external sources to have more control of histedits behavior, e.g. an external implementation of x/exec.

import-checker: check modules for pure Python build correctly Before this patch, "import-checker.py" just replaces "/" in specified filenames by ".". This makes modules for pure Python build belong to "mercurial.pure" package, and prevents "import-checker.py" from correctly checking about cyclic dependency in them. This patch discards "pure" component from fully qualified name of such modules. To avoid discarding "pure" from the module name of standard libraries unexpectedly, this patch allows "dotted_name_of_path" to discard "pure" only from Mercurial specific modules, which are specified via command line arguments.