perf tools: Add const.h to MANIFEST to make perf-tar-src-pkg work again

Fixes:
|make: *** No rule to make target `../../include/linux/const.h', needed by `builtin-annotate.o'.  Stop.

Cc: Ingo Molnar <mingo@elte.hu>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1324128938-17553-1-git-send-email-sebastian@breakpoint.cc


Signed-off-by: Sebastian Andrzej Siewior <sebastian@breakpoint.cc>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>