Show value of handle out of range in cvar_update
Includes some fixes from ioq3 in q_shared.c.
- "strcpy -> memmove as string does overlap which should be avoided according to the manpage. Thanks to Jacques Boscq."
- "include offending string in error message for varables that contain blacklisted characters"
- "Also send empty valued system cvars, fix proposed by DevHC"