Fix #345 - Workaround the unsurpported ALTER COLUMN in Redshift
Fix #345 - Workaround the unsurpported ALTER COLUMN in Redshift

Close #346

Squashed commit of the following:

commit af18b0497f3c77c64e413907d15eb86376dc1720
Author: Nan Jiang <njiang028@gmail.com>
Date:   Tue Apr 26 10:21:59 2016 -0400

    Fix the incompatible ddls for redshift in db migration

ncloudioj/splice,oyiptong/splice,ncloudioj/splice,ncloudioj/splice,oyiptong/splice,oyiptong/splice,ncloudioj/splice,mozilla/splice,oyiptong/splice,mozilla/splice,mozilla/splice,mozilla/splice