fix jfif resunit read

see https://github.com/jcupitt/libvips/issues/170

the previous fix just did exif resolution "none", we need jfif "none" as
well

ChangeLog

@@ -1,3 +1,6 @@
+8/9/14 started 7.40.9
+- support jfif resunit "none"
+
 8/9/14 started 7.40.8
 - fix configure on rhel6 [Lovell]
 - mono <-> rgb converters were not handling extra bands, thanks James

configure.ac

@@ -2,7 +2,7 @@
 
 # also update the version number in the m4 macros below
 
-AC_INIT([vips], [7.40.8], [vipsip@jiscmail.ac.uk])
+AC_INIT([vips], [7.40.9], [vipsip@jiscmail.ac.uk])
 # required for gobject-introspection
 AC_PREREQ(2.62)
 
@@ -18,7 +18,7 @@ AC_CONFIG_MACRO_DIR([m4])
 # user-visible library versioning
 m4_define([vips_major_version], [7])
 m4_define([vips_minor_version], [40])
-m4_define([vips_micro_version], [8])
+m4_define([vips_micro_version], [9])
 m4_define([vips_version],
           [vips_major_version.vips_minor_version.vips_micro_version])
 
@@ -38,7 +38,7 @@ VIPS_VERSION_STRING=$VIPS_VERSION-`date`
 #   binary interface changes not backwards compatible?: reset age to 0
 
 LIBRARY_CURRENT=38
-LIBRARY_REVISION=5
+LIBRARY_REVISION=6
 LIBRARY_AGE=0
 
 # patched into include/vips/version.h

libvips/foreign/jpeg2vips.c

@@ -744,6 +744,13 @@ read_jpeg_header( ReadJpeg *jpeg, VipsImage *out )
 #endif /*DEBUG*/
 
 		switch( cinfo->density_unit ) {
+		case 0:
+			/* None. Just set.
+			 */
+			xres = cinfo->X_density;
+			yres = cinfo->Y_density;
+			break;
+
 		case 1:
 			/* Pixels per inch.
 			 */