[MP] More robust fix for #450.

There are a number of ways that NaNs can reach the engine, and this is
then processed in R_FogFactor to produce an invalid index. This commit
provides a more robust fix for any NaNs which may cause a segfault.
[SP] More robust fix for R_FogFactor crash.
[MP] Fix #423: spectator bug after special move
[MP] Allow callvote kick to kick connecting clients.
Clean up kickother and giveother commands.  Plus allow them to work even if the host command caller is not alive.

This commit fixes #408.
[MP] Removed unused function G_ClientNumberFromName.
Also callvote clientkick range checks on the sv_maxclients value instead of absolute max.
[MP] Fix up ClientForString in g_svcmds.c
[MP] Tweak ClientNumberFromString to not use trinary operator.
[MP] Lets try fixing that one again.