Reimpl. the cvar alias system. Reimpl. the cvar hash table as a distinct type

Reimpl. the cvar alias system. Reimpl. the cvar hash table as a distinct type

It is now type-safe, cleaner, and doesn't require new static cvar_t's
for each alias. The hash table being implemented as a distinct type
allows multiple hashes to point to the same cvar without having to
create a new cvar_t for each alias.

git-svn-id: svn://svn.icculus.org/twilight/trunk/darkplaces@12652 d7cf8633-e32d-0410-b094-e92efae38249