perf tools: Fix backslash processing on trace print formats

The handling of backslashes was broken. It would stop parsing
when encountering one. Also, '\n', '\t', '\r' and '\\' were not
converted.

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: <20091014194357.521974680@goodmis.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>