spinlock to protect global static stuctures
added small parallel stress test
only include thread header if we are in the MULTI_THREAD environment
removed recursive spinlock and replaced it with regular stl recursive mutex
removed the parallel sdsl stress test.
enable spinlock/mutex protection by default
Merge pull request #45 from mpetri/spinlock-mm-ramfile

merge the spinlock and mutex protection to global static classes which allows using int_vectors in multiple threads.