fix warnings when building openssl with (gcc 3.3.1):

-Wmissing-prototypes -Wcomment -Wformat -Wimplicit -Wmain -Wmultichar
-Wswitch -Wshadow -Wtrigraphs -Werror -Wchar-subscripts
-Wstrict-prototypes -Wreturn-type -Wpointer-arith  -W -Wunused
-Wno-unused-parameter -Wuninitialized

ssl/d1_both.c

@@ -1229,7 +1229,7 @@ dtls1_min_mtu(void)
 static unsigned int 
 dtls1_guess_mtu(unsigned int curr_mtu)
 	{
-	int i;
+	size_t i;
 
 	if ( curr_mtu == 0 )
 		return g_probable_mtu[0] ;