Make it possible to use reasonable-synth in production

This allows to disable the xmass easter-egg for those who
don't celebrate x-mas.

libs/plugins/reasonablesynth.lv2/lv2.c

@@ -100,6 +100,7 @@ instantiate (const LV2_Descriptor*     descriptor,
 	synth_init(self->synth, rate);
 
 #ifndef PLATFORM_WINDOWS // easter egg is for sane platforms with native support for localtime_r only
+	if (!getenv("HEATHEN")) {
 		struct tm date;
 		time_t now;
 		time(&now);
@@ -108,6 +109,7 @@ instantiate (const LV2_Descriptor*     descriptor,
 			printf("reasonable synth.lv2 says: happy holidays!\n");
 			self->xmas = true;
 		}
+	}
 #endif
 
 	return (LV2_Handle)self;