wrlib: fixed prototype for 'RShutdown' in the public API header

Took opportunity to move it closer to the beginning of the file to improve
its visibility to users of the lib

wrlib/wraster.h

@@ -289,6 +289,11 @@ enum {
 #define RERR_INTERNAL		128    /* should not happen */
 
 
+/*
+ * Cleaning before application exit
+ */
+void RShutdown(void);
+
 /*
  * Returns a NULL terminated array of strings containing the
  * supported formats, such as: TIFF, XPM, PNG, JPEG, PPM, GIF
@@ -431,11 +436,7 @@ RImage *RRenderMultiGradient(unsigned width, unsigned height, RColor **colors,
 RImage *RRenderInterwovenGradient(unsigned width, unsigned height,
                                   RColor colors1[2], int thickness1,
                                   RColor colors2[2], int thickness2);
-/*
- * Cleaning
- */
 
-void RShutdown();
 
 /*
  * Convertion into X Pixmaps