Better altivec cvar handling. Should fix crashes at startup, or curious

people that toggle it on at runtime on a G3.

code/qcommon/qcommon.h

@@ -1033,6 +1033,8 @@ unsigned int Sys_ProcessorCount( void );
 
 int Sys_MonkeyShouldBeSpanked( void );
 
+qboolean Sys_DetectAltivec( void );
+
 /* This is based on the Adaptive Huffman algorithm described in Sayood's Data
  * Compression book.  The ranks are not actually stored, but implicitly defined
  * by the location of a node within a doubly-linked list */