perf diff: Add generic order option for compute sorting

Adding option 'o' to allow sorting based on the input file number. By
default (without -o option) the output is sorted on baseline.

Also removing '+' sorting support from -c option, because it's not
needed anymore.

Signed-off-by: Jiri Olsa <jolsa@redhat.com>
Reviewed-by: Namhyung Kim <namhyung@kernel.org>
Cc: Corey Ashford <cjashfor@linux.vnet.ibm.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/n/tip-l7dvhgt0azm7yiqg3fbn4dxw@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/Documentation/perf-diff.txt

@@ -75,8 +75,6 @@ OPTIONS
 -c::
 --compute::
         Differential computation selection - delta,ratio,wdiff (default is delta).
-        If '+' is specified as a first character, the output is sorted based
-        on the computation results.
         See COMPARISON METHODS section for more info.
 
 -p::
@@ -87,6 +85,10 @@ OPTIONS
 --formula::
         Show formula for given computation.
 
+-o::
+--order::
+       Specify compute sorting column number.
+
 COMPARISON
 ----------
 The comparison is governed by the baseline file. The baseline perf.data