perf_event_open() branch sample support

The following patch exercises some of the recent additions to the
perf_event_open() syscall.

The PERF_SAMPLE_WEIGHT and PERF_SAMPLE_DATA_SRC sample types were
added in Linux 3.10.

It also adds more complete support for PERF_SAMPLE_REGS_USER which was
added in Linux 3.7

Signed-off-by: Vince Weaver <vincent.weaver@maine.edu>