Keep correct type for immediate operands in comparisons

When calling metamethods for things like 'a < 3.0', which generates
the opcode OP_LTI, the C register tells that the operand was
converted to an integer, so that it can be corrected to float when
calling a metamethod.

This commit also includes some other stuff:
- file 'onelua.c' added to the project
- opcode OP_PREPVARARG renamed to OP_VARARGPREP
- comparison opcodes rewritten through macros

lopcodes.h

@@ -294,7 +294,7 @@ OP_CLOSURE,/*	A Bx	R(A) := closure(KPROTO[Bx])			*/
 
 OP_VARARG,/*	A C  	R(A), R(A+1), ..., R(A+C-2) = vararg		*/
 
-OP_PREPVARARG,/*A 	(adjust vararg parameters)			*/
+OP_VARARGPREP,/*A 	(adjust vararg parameters)			*/
 
 OP_EXTRAARG/*	Ax	extra (larger) argument for previous opcode	*/
 } OpCode;
@@ -331,6 +331,9 @@ OP_EXTRAARG/*	Ax	extra (larger) argument for previous opcode	*/
   C > 0 means the function is vararg and (C - 1) is its number of
   fixed parameters.
 
+  (*) In comparisons with an immediate operand, C signals whether the
+  original operand was a float.
+
 ===========================================================================*/