different probability distributions for spread (quake-style, solid circle, gaussian)

different probability distributions for spread (quake-style, solid circle, gaussian)
Currently, all is quake-style.
quake-style: http://rm.endoftheinternet.org/img/uploaded/6ad7218846a2a279987cbf230f6bab9e.jpg
circle:      http://rm.endoftheinternet.org/img/uploaded/06ce7e1fa72bd651cd7a0fd0b23f689e.jpg
gaussian:    http://rm.endoftheinternet.org/img/uploaded/8203aa325bc0bbce07d6329e97f44a35.jpg
The cvar doesn't change the standard deviation!

git-svn-id: svn://svn.icculus.org/nexuiz/trunk@8232 f962a42d-fe04-0410-a3ab-8c8b0445ebaa