errno/oserrno stuff is cleaned up, saved some bytes in dialog box functions

git-svn-id: svn://svn.cc65.org/cc65/trunk@775 b7a2c559-68d2-44c3-8de9-860c34a00d81

libsrc/geos/disk/dio_read.s

@@ -9,7 +9,7 @@
 ; sectnum_t - 16bit
 ;
 
-	.import		dio_params
+	.import		dio_params, __oserror
  	.export		_dio_read
 	.include "../inc/geossym.inc"
 	.include "../inc/jumptab.inc"
@@ -18,7 +18,7 @@
 
 	jsr dio_params
 	jsr ReadBlock
-	stx errno
+	stx __oserror
 	txa
 	rts