oops png gamma on save

the gamma on save was set to 1.0, incorrectly

TODO

@@ -1,5 +1,3 @@
-- png gamma is wrong on save?
-
 - add MATLAB write
 
 - sink.c, sinkdisc.c, sinkmemory.c all define this function:

libvips/format/im_vips2png.c

@@ -23,6 +23,8 @@
  * 	- set png resolution (thanks Zhiyu Wu)
  * 17/3/11
  * 	- update for libpng-1.5 API changes
+ * 28/3/11
+ * 	- argh gamma was wrong when viewed in firefox
  */
 
 /*
@@ -265,8 +267,6 @@ write_vips( Write *write, int compress, int interlace )
 		in->Xsize, in->Ysize, bit_depth, color_type, interlace_type, 
 		PNG_COMPRESSION_TYPE_DEFAULT, PNG_FILTER_TYPE_DEFAULT );
 
-	png_set_gAMA( write->pPng, write->pInfo, (float) 1.0 );
-
 	/* Set resolution. libpnbg uses pixels per meter.
 	 */
 	png_set_pHYs( write->pPng, write->pInfo,