start modification count for fresh cvars that are created as result of a cvar_get with 0, unless any "set" command called it, start with 1 then

this way we can differ between default-created cvars and explicitly set or via autogen loaded cvars
don't persist cvars that that weren't set, or loaded before; especially don't persist default cvar_get created cvars
this makes sure, that only cvars are persisted, that were at some point set by the user,
while it allows us to change default values of untouched cvars
or even remove old cvars without bothering the users about it, while not disturbing their right of customization
Optimize the calculation of visvis

visvis calculation is a significant part of map load time for large maps
remove unused sdl_vid.c, an unfinished directx port
[ci skip]
add a transience state keeping variable to all cvars and use it instead of the modification count for deciding whether or not to archive
display the transient state in the cvarlist
use Cvar_Set2 direcly with a NULL instead the resetValue during cvar restart, this will implicitly reset all cvars transient
rename field_t in g_spawn to not nameclash with field_t in qcommon.h and different client files
replace all found manually colored ERROR's and WARNING's with their text in strings with the precolored S_WARNING an S_ERROR define
this effectivly makes the presentation of errors and warnings more consistent
Servers listed as ‘IPX’ are really using IPv6 addresses. Fix display.
Merge branch 'cvar_defaults'
select entity number via always set entitystate, not via pointer arithmetics, that use a possibly soon removed reference
don't print (null) for unset entity names in etos()
replace all literally colored (i.e. with ^3 or ^1 instead of S_COLOR_YELLOW/RED) warnings and errors with the precolored S_WARNING and S_ERROR prefixes
replace several literal colorcodes with their defines
dont archive r_minimize
replace all cvar settings from the worldspawn with a function G_SpawnStringIntoCVar, which also makes sure that all are checked for presence first
Fix heartbeat sending (for servers going down).
Don't automatically drop UDPv6 ‘connectionless’ packets.

Without this, getstatus etc. would be unconditionally ignored if received
over IPv6.
add /cvar_clean as a more safe form of /cvar_restart, that resets archived cvars only if they are equal to their reset value (and as such it will remove them from the autogen.cfg if they are set to their default)