extfs: rpm: make it testable.
The way we make this helper testable is a bit different than with other
helpers:
While in other helpers we make it possible to override just one or two
variables, here we make it possible to inject a code snippet into it. This is a
more powerful approach which lets us override even functions, as will be shown
in a following patch.
(As for relocating the "AllTAGS=..." line: all non-declarative code needs to be
moved past our new injection point, or else this code won't be affected by the
injection. BTW, the "$1" on that line isn't used; a vestige from old days.)
Signed-off-by: Mooffie <mooffie@gmail.com>