Perform macro by replacing tokens in original list.

Perform macro by replacing tokens in original list.

We take the results of macro expansion and splice them into the
original token list over which we are iterating. This makes it easy
for function-like macro invocations to find their arguments since they
are simply subsequent tokens on the list.

This fixes the recently-introduced regressions (tests 55 and 56) and
also passes new tests 60 and 61 introduced to strees this feature,
(with macro-argument parentheses split between a macro value and the
textual input).