moved global variable "ob" to outputBuffer.h

This releases several include file dependencies.  As a side effect,
"CHUNK_SIZE" isn't defined by decoder_api.h anymore, so we have to
define it directly in the plugins which need it.  It just isn't worth
it to add it to the decoder plugin API.

src/inputPlugins/audiofile_plugin.c

@@ -26,6 +26,9 @@
 
 #include <audiofile.h>
 
+/* pick 1020 since its devisible for 8,16,24, and 32-bit audio */
+#define CHUNK_SIZE		1020
+
 static int getAudiofileTotalTime(char *file)
 {
 	int total_time;

src/inputPlugins/wavpack_plugin.c

@@ -28,6 +28,9 @@
 
 #include <wavpack/wavpack.h>
 
+/* pick 1020 since its devisible for 8,16,24, and 32-bit audio */
+#define CHUNK_SIZE		1020
+
 #define ERRORLEN 80
 
 static struct {