Imports: remove unused in translate/convert
Imports: remove unused in setup.py
Imports: remove unused in translate/storage/versioncontrol
Imports: remove unused in translate/storage
Imports: remove unused in translate/storage
Imports: remove unused in translate/tools
Imports: remove unused in translate/filters
Imports: remove unused in translate/search/indexing
Travis: --use-mirrors is deprecated in pip 1.5
Travis: Byte compile all .py files

Attempt to catch any syntax errors that maybe aren't caught by tests. Or
that are caught in files that aren't part of the setup scripts.
Travis: run setup.py building as a check
odf2xliff: Use a real with block
xml_extract: Use a real with block
misc: Drop context.py (fake with blocks)
misc: Drop contextlib, use stdlib contextlib instead
Docs: remove autodocs for removed modules

We forgot to remove the docs for:
translate/misc/{ini,context,contextlib}.py
Docs: include next release in doctree
Docs: report warnings as errors

This should allow us to catch autodoc related errors and files not in
the toctree.
Travis: move standalone pip installs to requirements/dev.txt
Travis: use pytest-xdist to test in subprocesses

This helps testing when using cPO, fPO and pypy that may segfault.