perf: make perf stat print user provided full event names

This patch changes the way perf stat prints event names at the end of a
run. Until now, it was trying to reconstruct the event name from its
encoding. The problem is that it would only print generic events without
their modifiers (u, k, pp).

This patch saves the event name as passed by the user in the evsel
struct and uses it to print the final event name.

This would also work in case perf is linked with a library (such as
libpfm4) which provides full PMU event tables.

$ perf stat -e cycles:u,cycles:k date
Wed Feb 16 14:58:52 CET 2011

 Performance counter stats for 'date':

            568600 cycles:u
           2779715 cycles:k

        0.001908182  seconds time elapsed

Cc: Arun Sharma <arun@sharma-home.net>
Cc: David S. Miller <davem@davemloft.net>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Robert Richter <robert.richter@amd.com>
Cc: Stephane Eranian <eranian@gmail.com>
LPU-Reference: <4d5bdc64.98a1df0a.7aa3.06c2@mx.google.com>
Signed-off-by: Stephane Eranian <eranian@google.com>
[ committer note: Fixed a merge problem with 023695d9 "Add cgroup support" ]
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>