brew-unpack: use extend instead of reopening Formula
brew-unpack: separate args passed to system
brew-unpack: don't chdir further than a normal install would

If we want to generate usable patches from inside the unpacked source,
then we should start from the same directory that a normal install
would start from.
gist 4.2.1
yaz: add test
exiftool 9.54
translate-toolkit: let scripts find python modules