perf hists: Link hist entries before inserting to an output tree

perf hists: Link hist entries before inserting to an output tree

For matching and/or linking hist entries, they need to be sorted by
given sort keys.  However current hists__match/link did this on the
output trees, so that the entries in the output tree need to be resort
before doing it.

This looks not so good since we have trees for collecting or collapsing
entries before passing them to an output tree and they're already sorted
by the given sort keys.  Since we don't need to print anything at the
time of matching/linking, we can use these internal trees directly
instead of bothering with double resort on the output tree.

Its only user - at the time of this writing - perf diff can be easily
converted to use the internal tree and can save some lines too by
getting rid of unnecessary resorting codes.

Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Acked-by: Jiri Olsa <jolsa@redhat.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lkml.kernel.org/r/1355128197-18193-3-git-send-email-namhyung@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>