The new test ../../tests/lean/run/tactic27.lean demonstrates why we need this feature. The tactic 'apply @refl' is actually 'apply @refl.{?l}'. It is used inside of a repeat tactical. Each iteration of the 'repeat' may need to use a different value for ?l. Before this commit, there was not way to say we want a fresh ?l each iteration.
Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
