New option "setparms" for 'collectgarbage'

The generational mode also uses the parameters for the incremental
mode in its major collections, so it should be easy to change those
parameters without having to change the GC mode.

lstate.h

@@ -264,12 +264,7 @@ typedef struct global_State {
   TValue l_registry;
   TValue nilvalue;  /* a nil value */
   unsigned int seed;  /* randomized seed for hashes */
-  lu_byte gcpgenminormul;  /* control minor generational collections */
-  lu_byte gcpmajorminor;  /* control shift major->minor */
-  lu_byte gcpminormajor;  /* control shift minor->major */
-  lu_byte gcppause;  /* size of pause between successive GCs */
-  lu_byte gcpstepmul;  /* GC "speed" */
-  lu_byte gcpstepsize;  /* GC granularity */
+  lu_byte gcparams[LUA_GCPN];
   lu_byte currentwhite;
   lu_byte gcstate;  /* state of garbage collector */
   lu_byte gckind;  /* kind of GC running */