Fix lack of random splay.

Since all child threads use the same seed, we need to reseed the random
generator with the pid so that we get a new "random" number.  Also
using mt_rand instead of rand since it is faster.
Merge branch 'jpirkey-use-mt_rand-for-splay-calculation' into master-clean
Merge branch 'master-clean' into master-clean-composer-test