build: let TWRP eat zips too

This allows us to sideload zips regardless of the recovery in place.

Change-Id: I5e95614e545a617737fcc27fd892f42c29a06f9b
Merge "build: let TWRP eat zips too" into cm-10.2
Merge branch 'cm-10.2' of https://github.com/CyanogenMod/android_build into jb-mr2