wrlib: new headers to contain definition of internal stuff

Using local function prototype redefinition is dangerous, now a single
prototype is seen in all the files that are concerned.

Signed-off-by: Christophe CURIS <christophe.curis@free.fr>

wrlib/Makefile.am

@@ -33,11 +33,13 @@ libwraster_la_SOURCES = 	\
 	context.c 	\
 	misc.c 		\
 	scale.c		\
+	scale.h		\
 	rotate.c	\
 	flip.c		\
 	convolve.c	\
 	save_xpm.c	\
 	xutil.c		\
+	xutil.h		\
 	load_ppm.c
 
 if USE_GIF