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/url.c

@@ -130,10 +130,7 @@ int curl_win32_idn_to_ascii(const char *in, char **out);
 #include "pipeline.h"
 #include "dotdot.h"
 #include "strdup.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"