perf tools: Add +field argument support for --field option

Adding support to add field(s) to default field order via using the '+'
prefix, like for report:

  $ perf report
  Samples: 10  of event 'cycles', Event count (approx.): 4463799
  Overhead  Command  Shared Object      Symbol
    32.40%  ls       [kernel.kallsyms]  [k] filemap_fault
    28.19%  ls       [kernel.kallsyms]  [k] get_page_from_freelist
    23.38%  ls       [kernel.kallsyms]  [k] enqueue_entity
    15.04%  ls       [kernel.kallsyms]  [k] mmap_region

  $ perf report -F +period,sample
  Samples: 10  of event 'cycles', Event count (approx.): 4463799
  Overhead        Period       Samples  Command  Shared Object      Symbol
    32.40%       1446493             1  ls       [kernel.kallsyms]  [k] filemap_fault
    28.19%       1258486             1  ls       [kernel.kallsyms]  [k] get_page_from_freelist
    23.38%       1043754             1  ls       [kernel.kallsyms]  [k] enqueue_entity
    15.04%        671160             1  ls       [kernel.kallsyms]  [k] mmap_region

Works in general for commands using --field option.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Cc: Corey Ashford <cjashfor@linux.vnet.ibm.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Jean Pihet <jean.pihet@linaro.org>
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/r/1408715919-25990-2-git-send-email-jolsa@kernel.org


Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>