The kernel folks are referring to "Performance Counters for Linux" (the title of the original proposal posted on LKML) as just perf_counters now, and the user-space tool they've developed as "perf". I think they chose to refer to it as perf_counters because the bulk of the code is contained in kernel/perf_counter.c in the kernel source. So only a few of the kernel developers will call it PCL, and those are the ones from IBM who hadn't followed the LKML discussion much.
To straighten things out on the PAPI side, we probably ought to change the name of the PAPI substrate to perf_counters rather than PCL, to reduce the confusion.... though it might make it harder to distinguish perfctr from perf_counters!
As far as a standard library goes, that's still up in the air. Peter Zijlstra was working on a library called libperf, which will I think provide some of the same ability as Stephane Eranian's libpfm, but oriented a bit differently since it will only support perf_counters.
Stephane Eranian was also working on a new version of libpfm to support perf_counters.
I'm not clear on the current status of these two projects.
In the case of libperf, it's possible it may get shipped with the kernel source, like the perf tool. The perf tool is the only case where the source for a user-space tool is in the kernel's git tree. When you download a 2.6.31 kernel, you get perf too.