enable strip chopping on TIFF load

see https://github.com/libvips/libvips/discussions/2322

thanks DavidStorm

ChangeLog

@@ -3,6 +3,7 @@
 - update libtool support in configure.ac 
 - more startup info if VIPS_INFO is set
 - command-line programs set glib prgname (no longer set for you by VIPS_INIT)
+- enable strip chopping for TIFF read [DavidStorm]
 
 14/8/20 started 8.11
 - add vips_jpegload_source() and vips_svgload_source() to public C API

libvips/foreign/tiff.c

@@ -212,7 +212,14 @@ vips__tiff_openin_source( VipsSource *source )
 	if( vips_source_rewind( source ) )
 		return( NULL );
 
-	if( !(tiff = TIFFClientOpen( "source input", "rm",
+	/* Disable memory mapped input -- it chews up VM and the performance
+	 * gain is very small. 
+	 *
+	 * C enables strip chopping: very large uncompressed strips are 
+	 * chopped into c. 8kb chunks. This can reduce peak memory use for 
+	 * this type of file.
+	 */
+	if( !(tiff = TIFFClientOpen( "source input", "rmC",
 		(thandle_t) source,
 		openin_source_read,
 		openin_source_write,