NOCACHE was not being set on OS X

mmap() on OS X caches too much and we were not turning it off correctly

ChangeLog

@@ -1,3 +1,7 @@
+12/10/11 started 7.26.6
+- NOCACHE was not being set correctly on OS X causing performance 
+  problems with large files
+
 12/10/11 started 7.26.5
 - jpeg read/write copies over XMP data
 

configure.in

@@ -6,7 +6,7 @@ AC_CONFIG_MACRO_DIR(m4)
 # user-visible library versioning
 m4_define([vips_major_version], [7])
 m4_define([vips_minor_version], [26])
-m4_define([vips_micro_version], [5])
+m4_define([vips_micro_version], [6])
 m4_define([vips_version],
           [vips_major_version.vips_minor_version.vips_micro_version])
 
@@ -29,7 +29,7 @@ PACKAGE=vips
 #   interface changes not backwards compatible?: reset age to 0
 
 LIBRARY_CURRENT=30
-LIBRARY_REVISION=4
+LIBRARY_REVISION=5
 LIBRARY_AGE=15
 
 AM_INIT_AUTOMAKE($PACKAGE,$VERSION)

libvips/iofuncs/mapfile.c

@@ -176,7 +176,7 @@ vips__mmap( int fd, int writeable, size_t length, gint64 offset )
 	 * LARGEFILE.
 	 */
 
-	baseaddr = mmap( 0, length, prot, MAP_SHARED, fd, (off_t) offset );
+	baseaddr = mmap( 0, length, prot, flags, fd, (off_t) offset );
 	if( baseaddr == MAP_FAILED ) { 
 		vips_error_system( errno, "vips_mapfile", 
 			"%s", _( "unable to mmap" ) );