perf trace: Add 'trace' alias to 'perf trace'

perf trace: Add 'trace' alias to 'perf trace'

Make 'perf trace' more accessible by aliasing it to just 'trace':

  [root@zoo linux]# trace --duration 15 -a -e futex sleep 1
   110.092 (16.188 ms): libvirtd/1166 futex(uaddr: 0x185b344, op: WAIT|PRIV, val: 174293                    ) = 0
   110.101 (15.903 ms): libvirtd/1171 futex(uaddr: 0x185b3dc, op: WAIT|PRIV, val: 139265                    ) = 0
   111.594 (15.776 ms): libvirtd/1165 futex(uaddr: 0x185b344, op: WAIT|PRIV, val: 174295                    ) = 0
   111.610 (15.969 ms): libvirtd/1169 futex(uaddr: 0x185b3dc, op: WAIT|PRIV, val: 139267                    ) = 0
   113.556 (16.216 ms): libvirtd/1168 futex(uaddr: 0x185b3dc, op: WAIT|PRIV, val: 139269                    ) = 0
   291.265 (199.508 ms): chromium-brows/15830 futex(uaddr: 0x7fff2986bcb4, op: WAIT_BITSET|PRIV|CLKRT, val: 1, utime: 0x7fff2986bab0, val3: 4294967295) = -1 ETIMEDOUT Connection timed out
     360.354 (69.053 ms): chromium-brows/15830 futex(uaddr: 0x7fff2986bcb4, op: WAIT_BITSET|PRIV|CLKRT, val: 1, utime: 0x7fff2986bab0, val3: 4294967295) = -1 ETIMEDOUT Connection timed out
  [root@zoo linux]#

I.e. looking for futex calls that take at least 15ms, system wide, during a one
second window. Now to get callchains into 'trace' to figure out what are those
locks :-)

Requested-by: Ingo Molnar <mingo@kernel.org>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lkml.kernel.org/n/tip-ch4smqz8b5fmgrte7c5e4fuw@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>