match.c: revert bad commits.

This contains two reverts, folded into one.

"txr: spurious retention in @(next)."
commit fe1e960389a89f481d46c02aa040fdc762da735f.

"txr: avoid by-value match_files_ctx passing."
commit 3d7330b827d6e9cc0d9e87edd30388374cb45900.

These are dependent. The second of these two (i.e. the one
that was done first) is the problematic one. By-reference
passing of contexts means contexts become shared objects
between callers and callees. But this is incorrect, because
mutations are going on, like c->spec = rest(c->spec) or
c->data = rest(c->data). These mutations were done under the
assumption of safety: that the caller is not affected due to
by-value semantics of the entire context.

0 files changed, 0 insertions, 0 deletions