properly rename internal [v]snprintf() functions

Otherwise it clashes when we want to re-introduce the `xmpp_` prefix'ed
versions.

Signed-off-by: Steffen Jaeckel <jaeckel-floss@eyet-services.de>

src/snprintf.h

@@ -20,16 +20,14 @@
 #endif
 
 #ifdef HAVE_SNPRINTF
-#define xmpp_snprintf snprintf
+#define strophe_snprintf snprintf
 #else
-#define xmpp_snprintf strophe_snprintf
 int strophe_snprintf(char *str, size_t count, const char *fmt, ...);
 #endif
 
 #ifdef HAVE_VSNPRINTF
-#define xmpp_vsnprintf vsnprintf
+#define strophe_vsnprintf vsnprintf
 #else
-#define xmpp_vsnprintf strophe_vsnprintf
 int strophe_vsnprintf(char *str, size_t count, const char *fmt, va_list arg);
 #endif