meta_path copying fails on ZMQ socket due to SixMetaPathImporter

The BasicProfile deepcopies the `sys.meta_path` (why do we need to modify this in the first place?) which, in the context of the "six" Python 2-3 compatibility module leads to trying to copy a ZMQ socket, which fails (and would be questionable in any case, as deepcopy doesn't copy a regular socket).

A possible workaround is to register a special copier via the `copy_reg` module, to handle six's MetaPathImporter.

https://docs.python.org/2/library/copy_reg.html