Makes it easier to specify both events and syscalls (to be formatter
strace-like), i.e. previously one would have to do:

  # perf trace -e nanosleep --event sched:sched_switch usleep 1

Now it is possible to do:

  # perf trace -e nanosleep,sched:sched_switch usleep 1
     0.000 ( 0.021 ms): usleep/17962 nanosleep(rqtp: 0x7ffdedd61ec0) ...
     0.021 (         ): sched:sched_switch:usleep:17962 [120] S ==> swapper/1:0 [120])
     0.000 ( 0.066 ms): usleep/17962  ... [continued]: nanosleep()) = 0
  #

The old style --expr and using both -e and --event continues to work.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Milian Wolff <milian.wolff@kdab.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Wang Nan <wangnan0@huawei.com>
Link: http://lkml.kernel.org/n/tip-ieg6bakub4657l9e6afn85r4@git.kernel.orgSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>