Flexible limit for use of registers by constructors

Instead of a fixed limit of 50 registers (which, in a bad worst case,
can limit the nesting of constructors to 5 levels), the compiler
computes an individual limit for each constructor based on how many
registers are available when it runs. This limit then controls the
frequency of SETLIST instructions.

lopcodes.h

@@ -406,7 +406,4 @@ LUAI_DDEC(const lu_byte luaP_opmodes[NUM_OPCODES];)
     (((mm) << 7) | ((ot) << 6) | ((it) << 5) | ((t) << 4) | ((a) << 3) | (m))
 
 
-/* number of list items to accumulate before a SETLIST instruction */
-#define LFIELDS_PER_FLUSH	50
-
 #endif