Check bash version instead of OS for bash completion

The bash completion script requires bash 4.0

Change-Id: Id81a42585b1d2cb568cb1b8f602f2bb447bef214
Consolidate bash version checks

There were two checks for bash version, the 2nd was superfluous; this
patch removes the duplicate checks, and shifts the bash version check to
being back after the "are we in bash" check.

Change-Id: I57ff8c1fedce80f739c06643d2976d2c1465db1b
Merge branch 'cm-10.1' of github.com:CyanogenMod/android_build into cm-10.1