parsers: fix a memleak, and add a clearcaches method to the index
This change also fixes a nasty memory leak: previously, self->caches
was not being freed.
The new clearcaches method lets us benchmark with finer granularity,
as it lets us separate the cost of loading a revlog index from those
of populating and accessing the cache data structures.
$ "$TESTDIR/hghave" serve || exit 80
$ hg init test
$ cd test
$ cat > .hg/hgrc <<EOF
> [extensions]
> interhg =
>
> [interhg]
> issues = s|Issue(\d+)|<a href="http://bts.example.org/issue\1">Issue\1</a>|
>
> # yes, 'x' is a weird delimiter...
> markbugs = sxbugx<i class="\x">bug</i>x
> EOF
$ touch foo
$ hg add foo
$ hg commit -d '1 0' -m 'Issue123: fixed the bug!'
$ hg serve -n test -p $HGPORT -d --pid-file=hg.pid -A access.log -E errors.log
$ cat hg.pid >> $DAEMON_PIDS
log
$ "$TESTDIR/get-with-headers.py" localhost:$HGPORT '/' | grep bts
<td class="description"><a href="/rev/1b0e7ece6bd6"><a href="http://bts.example.org/issue123">Issue123</a>: fixed the <i class="x">bug</i>!</a><span class="branchhead">default</span> <span class="tag">tip</span> </td>
errors
$ cat errors.log