Summary:
D13853115 adds `edenscm/` to `sys.path` and code still uses `import mercurial`.
That has nasty problems if both `import mercurial` and
`import edenscm.mercurial` are used, because Python would think `mercurial.foo`
and `edenscm.mercurial.foo` are different modules so code like
`try: ... except mercurial.error.Foo: ...`, or `isinstance(x, mercurial.foo.Bar)`
would fail to handle the `edenscm.mercurial` version. There are also some
module-level states (ex. `extensions._extensions`) that would cause trouble if
they have multiple versions in a single process.
Change imports to use the `edenscm` so ideally the `mercurial` is no longer
imported at all. Add checks in extensions.py to catch unexpected extensions
importing modules from the old (wrong) locations when running tests.
Reviewed By: phillco
Differential Revision: D13868981
fbshipit-source-id: f4e2513766957fd81d85407994f7521a08e4de48
Extensions sometimes wants to add other information in the default log output
format (when no templating is used).
Add an empty function named '_exthook' for easing the extension life.
Extensions will be able to wrap this function and collaborate to display
additional information.
Exthook is called after displaying troubles and just before displaying the
files, extra and description.
Add a new test file to test it and not pollute other test files.
