Re: [v3] parallel mode

This is now in. The final patch is as attached.

Differences from what was previously posted:

1) --disable-gomp now works
2) __gnu_sequential doxygen markup fix
3) added check-performance-parallel
4) moved mismatch into parallel/algobase.h, from parallel/algo.h.

There is one regression in parallel mode, in
25_algo/lexicographical_compare. Everything else is fine.

tested x86/linux
tested x86_64/linux

tested parallel x86/linux
tested parallel x86_64/linux

tested performance x86/linux
tested performance-parallel x86/linux

tested x86/darwin

I'm still sorting out the darwin parallel testing.

best,
benjamin