Backport docs highlighting check monkey-patch for Sphinx starting from v0.6.6

Currently host that builds documentation uses Sphinx v1.0.7.

This monkey-patched tested with Sphinx (few) versions starting from v1.0,
because Buildbot's master/docs/bbdocs/ext.py depends on features
introduced there (Sphinx Domains).
Fix highligting issue with Sphinx 1.0 (and in 1.0.7)

Old Sphinx versions not highlighted unparsable Python code (new one
does).
Merge branch 'backport_docs_highlighting_monkey_patch' of git://github.com/vrutsky/buildbot