It seems that the perf_counter_open system call was renamed to

It seems that the perf_counter_open system call was renamed to
perf_event_open some time after we added it, so correct the name
wherever it appears to match the current kernel source.

Also fixup the PRE handler to do the check correctly, using the
size field of the structure to work out how much data there is.

git-svn-id: svn://svn.valgrind.org/valgrind/trunk@11804