Change useexisting to extend_existing to fix deprecation warnings.

This squelches a deprecation warning during installation.

We're already using extend_existing in other places, so I don't
think this causes any new version compatibility issues.

Fixes bug 925609.  (Already marked fixed, but this hits more cases.)

Includes some merges with a whitespace-cleanup fix.

Change-Id: Ia166e9184ed3e13753c5669a1006a3711738319a
Merge "Change useexisting to extend_existing to fix deprecation warnings." into stable/folsom