isolated sources of random values. Add normal and exponential distributions. Add some tests for the normal and exponential distributions. R=rsc APPROVED=rsc DELTA=1005 (904 added, 80 deleted, 21 changed) OCL=35501 CL=35779
R=rsc APPROVED=rsc DELTA=637 (318 added, 318 deleted, 1 changed) OCL=35534 CL=35536
to whole-package compilation. R=r OCL=33070 CL=33101
tests: all.bash passes, gobuild still works, godoc still works. R=rsc OCL=30096 CL=30102