perf tools: Handle - and + in parsing trace print format

The opterators '-' and '+' are not handled in the trace print
format.

To do: '++' and '--'.

Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
LKML-Reference: <20091014194400.330843045@goodmis.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>