fix various typos

thanks dg1727

see https://github.com/jcupitt/libvips/issues/277

libvips/colour/scRGB2BW.c

@@ -270,7 +270,7 @@ vips_scRGB2BW_init( VipsscRGB2BW *scRGB2BW )
  *
  * @depth: depth of output image in bits
  *
- * Convert an scRGB image to sRGB. Set @depth to 16 to get 16-bit output.
+ * Convert an scRGB image to greyscale. Set @depth to 16 to get 16-bit output.
  *
  * If @depth is 16, any extra channels after RGB are 
  * multiplied by 256. 

libvips/include/vips/foreign.h

@@ -1,10 +1,10 @@
-/* Base type for supported image foreigns. Subclass this to add a new
- * foreign.
+/* Base type for supported image formats. Subclass this to add a new
+ * format.
  */
 
 /*
 
-    This foreign is part of VIPS.
+    This file is part of VIPS.
     
     VIPS is free software; you can redistribute it and/or modify
     it under the terms of the GNU Lesser General Public License as published by
@@ -25,7 +25,7 @@
 
 /*
 
-    These foreigns are distributed with VIPS - http://www.vips.ecs.soton.ac.uk
+    These files are distributed with VIPS - http://www.vips.ecs.soton.ac.uk
 
  */
 
@@ -140,7 +140,7 @@ typedef struct _VipsForeignLoad {
 	VipsImage *out;
 
 	/* The behind-the-scenes real image we decompress to. This can be a
-	 * disc foreign or a memory buffer. This must be set by ->load().
+	 * disc file or a memory buffer. This must be set by ->load().
 	 */
 	VipsImage *real;
 

libvips/include/vips/image.h

@@ -89,7 +89,8 @@ typedef enum {
 	VIPS_INTERPRETATION_RGB16 = 25,
 	VIPS_INTERPRETATION_GREY16 = 26,
 	VIPS_INTERPRETATION_MATRIX = 27,
-	VIPS_INTERPRETATION_scRGB = 28
+	VIPS_INTERPRETATION_scRGB = 28,
+	VIPS_INTERPRETATION_LAST = 29
 } VipsInterpretation;
 
 typedef enum {

libvips/iofuncs/enumtypes.c

@@ -540,6 +540,7 @@ vips_interpretation_get_type( void )
 			{VIPS_INTERPRETATION_GREY16, "VIPS_INTERPRETATION_GREY16", "grey16"},
 			{VIPS_INTERPRETATION_MATRIX, "VIPS_INTERPRETATION_MATRIX", "matrix"},
 			{VIPS_INTERPRETATION_scRGB, "VIPS_INTERPRETATION_scRGB", "scrgb"},
+			{VIPS_INTERPRETATION_LAST, "VIPS_INTERPRETATION_LAST", "last"},
 			{0, NULL, NULL}
 		};