Revert "Refs #294. Used pthread_atfork to avoid hang after a Unix fork."

This reverts commit 3617c22a5679c52b1e760d739d76a7bde9e84d35.
FIX #294: make OpenBLAS thread-pool resilient to fork via pthread_atfork
Make sure that fork_test.c is not built under windows
Do not reference pthread_atfork under windows
Merge pull request #343 from ogrisel/fix-294-fork-safe-pthread

FIX #294: fork-safe pthread mode