perf evsel: Subclassing

perf evsel: Subclassing

Provide a method to be called at tool start to config the perf_evsel
instance size, together with optional constructor and destructor.

This will be used so that perf_evsel doesn't always include a struct
hists, tools that works with hists/hist_entries, like report, top and
annotate, will, at start, tell the evsel class the size they need per
instance.

v2: Don't use exit as a name of a member of function parameter, as this
    breaks the build on at least fedora14 and rhel6.

Cc: Adrian Hunter <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: David Ahern <[email protected]>
Cc: Don Zickus <[email protected]>
Cc: Frederic Weisbecker <[email protected]>
Cc: Jean Pihet <[email protected]>
Cc: Jiri Olsa <[email protected]>
Cc: Mike Galbraith <[email protected]>
Cc: Namhyung Kim <[email protected]>
Cc: Paul Mackerras <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Stephane Eranian <[email protected]>
Link: http://lkml.kernel.org/n/[email protected]
Signed-off-by: Arnaldo Carvalho de Melo <[email protected]>