Augments a tactic's theorem list with the assumptions.
DESCRIPTION
If tac is a tactic that expects a list of theorems as its arguments, e.g.
MESON_TAC, REWRITE_TAC or SET_TAC, then ASM tac converts it to a tactic
where that list is augmented by the goal's assumptions.
FAILURE CONDITIONS
Never fails (though the resulting tactic may do).
EXAMPLE
The inbuilt ASM_REWRITE_TAC is in fact defined as just ASM REWRITE_TAC.