Enable "sync -c" default for repo

back ported from 259d8c3eb4309315087b8ef8b64ec90eb9861025
also it makes sync -j "4"

Change-Id: I2bba87c736336662d1235fdb9130d76da44a5404
Merge branch 'gingerbread' of git://github.com/CyanogenMod/android into gingerbread