Move pgettext_aux() declaration earlier

Some compilers get upset if a declaration comes after the definition.

vncviewer/i18n.h

 #ifndef _I18N_H
 #define _I18N_H 1
 
-#include "gettext.h"
-
 /* Need to tell gcc that pgettext() doesn't screw up format strings */
 #ifdef __GNUC__
 static const char *
               int category) __attribute__ ((format_arg (3)));
 #endif
 
+#include "gettext.h"
+
 #define _(String) gettext (String)
 #define p_(Context, String) pgettext (Context, String)
 #define N_(String) gettext_noop (String)