Explain groups for DeprecatedOpts

The patch extends the documentation for `DeprecatedOpt` and explains
that group==None means the deprecated name will be looked up in the same
group.

Change-Id: I54ba414d6a6862e1b00dfbf589563ef9f4df5cf3
Work toward Python 3.4 support and testing

Change-Id: Iadb1b695b8314d385716619561a1604a41f6c8d5
Merge "Work toward Python 3.4 support and testing"
Merge "Explain groups for DeprecatedOpts"