A lot of checkers need access to the token stream, but they all tokenize the
source code again in BaseRawChecker.process_module. This change introduces
a new checker type ITokenChecker, for which the token stream is created
exactly once in PyLinter, and then injected into all registered checkers.
Astng will try to find the right encoding and provide the right "stream"
interface for the Pylint checkers.
Reading a stream with the wrong encoding in py3k will generate a UnicodeError.
The introduced a 'F0010' failure should maybe be replaced by E0501, E0502 and
F0002? However, can we call 'unexpected errors' the ASTNGBuildingExceptions
that we raise in logilab.astng.builder?
