Allow 'perf record' to split its output into multiple files.

For example:

  # ~/perf record -a --timestamp-filename --switch-output &
  [1] 10763
  # kill -s SIGUSR2 10763
  [ perf record: dump data: Woken up 1 times ]
  # [ perf record: Dump perf.data.2015122622314468 ]

  # kill -s SIGUSR2 10763
  [ perf record: dump data: Woken up 1 times ]
  # [ perf record: Dump perf.data.2015122622314762 ]

  # kill -s SIGUSR2 10763
  [ perf record: dump data: Woken up 1 times ]
  #[ perf record: Dump perf.data.2015122622315171 ]

  # fg
  perf record -a --timestamp-filename --switch-output
  ^C[ perf record: Woken up 1 times to write data ]
  [ perf record: Dump perf.data.2015122622315513 ]
  [ perf record: Captured and wrote 0.014 MB perf.data.<timestamp> (296 samples) ]

  # ls -l
  total 920
  -rw------- 1 root root 797692 Dec 26 22:31 perf.data.2015122622314468
  -rw------- 1 root root  59960 Dec 26 22:31 perf.data.2015122622314762
  -rw------- 1 root root  59912 Dec 26 22:31 perf.data.2015122622315171
  -rw------- 1 root root  19220 Dec 26 22:31 perf.data.2015122622315513

Signed-off-by: Wang Nan <wangnan0@huawei.com>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Zefan Li <lizefan@huawei.com>
Cc: pi3orama@163.com
Link: http://lkml.kernel.org/r/1461178794-40467-4-git-send-email-wangnan0@huawei.com


Signed-off-by: He Kuang <hekuang@huawei.com>
[ Added man page entry, used the re-synthesize patch in this series as a fixup ]
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>