input_stream: use "goffset" instead of "off_t"

The "off_t" type may change when you enable or disable large file
support on 32 bit platforms.  This caused severe ABI problems within
MPD when we enabled LFS for the first time: two sources included
config.h and sys/types.h in different order, and had different off_t
sizes - leading to memory corruption because of ABI incompatibility.
This patch attempts to get rid of all public "off_t" uses: it removes
"off_t" from the input_stream ABI/API, and switches to GLib's 64 bit
"goffset" type.  This may hurt 32 bit embedded platforms a tiny bit,
but that's not even measurable.

src/input_stream.h

@@ -20,14 +20,12 @@
 #ifndef MPD_INPUT_STREAM_H
 #define MPD_INPUT_STREAM_H
 
-#include "config.h"
+#include <glib.h>
 
 #include <stddef.h>
 #include <stdbool.h>
 #include <sys/types.h>
 
-struct input_stream;
-
 struct input_stream {
 	/**
 	 * the plugin which implements this input stream
@@ -58,12 +56,12 @@ struct input_stream {
 	/**
 	 * the size of the resource, or -1 if unknown
 	 */
-	off_t size;
+	goffset size;
 
 	/**
 	 * the current offset within the stream
 	 */
-	off_t offset;
+	goffset offset;
 
 	/**
 	 * the MIME content type of the resource, or NULL if unknown
@@ -108,7 +106,7 @@ input_stream_close(struct input_stream *is);
  * @param whence the base of the seek, one of SEEK_SET, SEEK_CUR, SEEK_END
  */
 bool
-input_stream_seek(struct input_stream *is, off_t offset, int whence);
+input_stream_seek(struct input_stream *is, goffset offset, int whence);
 
 /**
  * Returns true if the stream has reached end-of-file.