build: let TWRP eat zips too

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

Change-Id: I5e95614e545a617737fcc27fd892f42c29a06f9b

Conflicts:
	envsetup.sh
envsetup: do not print an error if complete fails

complete is a bashism; so it will fail on other shells. Avoid printing
an error if that is the case.

Change-Id: Id6d6311792f409cc3a697c7a2bb003863f1afe60
envsetup: drop unnecesary exports

export -f is a bashism and we don't actually need it, so lets remove it.

Conflicts:
	envsetup.sh

Change-Id: I9228cef0c4a9543b3d34fdc39a368ad0238431e2

Conflicts:
	envsetup.sh
envsetup: Mark zsh as compatible

Basic functionality has been tested on zsh 5.0.2 and has been found to
work correctly.

Change-Id: I02e5e3bedf56b43104c280d9737ae7b334357643