This is a rebased final version of a proposed solution to fix
issues #932, #1104 & #1180. Following changes have been done:
* Implemented a new class `PipXmlrpcTransport` using a
contained `PipSession` object.
* Modified the `pip/commands/search.py` to make use of the
`PipXmlrpcTransport` class.
* Properly initialized options for testing `SearchCommand`:
- Changed `options_mock` to an `options` object built from
`parse_args`, to properly initialize default options.
57f2d47b84