mprintf.h: remove #ifdef CURLDEBUG

... and as a consequence, introduce curl_printf.h with that re-define
magic instead and make all libcurl code use that instead.

lib/curl_addrinfo.c

@@ -50,15 +50,12 @@
 #include "curl_addrinfo.h"
 #include "inet_pton.h"
 #include "warnless.h"
-
-#define _MPRINTF_REPLACE /* use our functions only */
-#include <curl/mprintf.h>
-
+#include "curl_printf.h"
 #include "curl_memory.h"
+
 /* The last #include file should be: */
 #include "memdebug.h"
 
-
 /*
  * Curl_freeaddrinfo()
  *