only LOG() the DPI when it changes, DLOG() it otherwise (Thanks lkraav)

This avoids flooding stdout every time some text (e.g. a window
decoration) is drawn, yet leaves the message in place when it’s actually
relevant (upon DPI changes).

fixes #1115

i3bar/include/util.h

@@ -48,6 +48,9 @@
     } \
 } while (0)
 
+#if defined(DLOG)
+#undef DLOG
+#endif
 /* Use cool logging-macros */
 #define DLOG(fmt, ...) do { \
     if (config.verbose) { \