Added gcc option '-Wconversion'

No warnings for standard numerical types. Still pending alternative
numerical types.

lzio.h

@@ -32,7 +32,7 @@ typedef struct Mbuffer {
 #define luaZ_sizebuffer(buff)	((buff)->buffsize)
 #define luaZ_bufflen(buff)	((buff)->n)
 
-#define luaZ_buffremove(buff,i)	((buff)->n -= (i))
+#define luaZ_buffremove(buff,i)	((buff)->n -= cast_sizet(i))
 #define luaZ_resetbuffer(buff) ((buff)->n = 0)