logilab-common #235354 modutils: speed up file_from_modpath by using an abspath cache [in-progress]

A profile of pylint running against a file from our codebase blamed almost half a second on normpath, almost all of it coming from abspath via _module_file. We have a somewhat lengthy sys.path, and calling abspath on everything in it for every import added up.

See https://bitbucket.org/logilab/logilab-common/pull-request/3/use-a-cache-when-abspathing-syspath/ for the original pull request.

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patch[modutils] Use a cache when abspathing sys.path for file_from_modpath. [in-progress]