Make unaligned centered alignment optional.

Make unaligned centered alignment optional.

Centered alignment was recently made unaligned by
e99c5a3f113bbc1b8f8db996b4b0d5715eea2d89.  This has the side-effect
of sometimes making items appear fuzzy due to sub-pixel alignment.
Since we have two conflicting goals, make this behavior configuarable.

Change-Id: I5ed0e9532a64f4a986d148044f5871a7ec970f5f
Reviewed-by: Bea Lam <bea.lam@nokia.com>