Added NetBSD processor affinity support.

[yazshel]

Hi,

I've added processor affinity support for NetBSD to xhprof. I've tested the changes on Linux and MacOS but not FreeBSD (as I don't currently have have access to a FreeBSD box).

A couple of notes:

• In the GET_AFFINITY / SET_AFFINITY macros, I'm ignoring pid and calling pthread_self() instead. It's only ever currently called with a pid argument of 0 (ie. self) anyway...
• I've changed all direct references to cpu_set_t to be pointers, and are allocating memory for the cpu_set_t/cpuset_t structure. This is because on NetBSD, the cpuset_t structure is declared but not defined in the headers. NetBSD provides cpuset_* functions to create, manipulate and sizeof cpuset_t structures.
• There is currently one test failing on NetBSD ... I'm not sure that it's related to the processor affinity stuff though. It's tests/xhprof_005 an it fails with the following output. Without a good understanding of how the usleep stuff works, I'm a bit unsure of what might be going on here; any ideas?

Verifying sleep_10000_micro...
Failed sleep_10000_micro. Expected: 10000 microsecs. Actual: 20018 microsecs.
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Verifying sleep_20000_micro...
Failed sleep_20000_micro. Expected: 20000 microsecs. Actual: 29949 microsecs.
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Verifying sleep_50000_micro...
OK: sleep_50000_micro
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Let me know if there is anything else you'd like me to change as part of this pull request.

Cheers,

Timshel