Fix memory leaks in record_out() and record_send().

record_out() leaks memory: it fails to free the strings returned by the
per-column output functions, and also is careless about detoasted values.
This results in a query-lifespan memory leakage when returning composite
values to the client, because printtup() runs the output functions in the
query-lifespan memory context.  Fix it to handle these issues the same way
printtup() does.  Also fix a similar leakage in record_send().

(At some point we might want to try to run output functions in
shorter-lived memory contexts, so that we don't need a zero-leakage policy
for them.  But that would be a significantly more invasive patch, which
doesn't seem like material for back-patching.)

In passing, use appendStringInfoCharMacro instead of appendStringInfoChar
in the innermost data-copying loop of record_out, to try to shave a few
cycles from this function's runtime.

Per trouble report from Carlos Henrique Reimer.  Back-patch to all
supported versions.