img test: set old timestamp on source file that will change

This is so that the test will pass even if it takes less than 1 second.

debian/changelog

@@ -2,6 +2,8 @@ ikiwiki (3.20150611) UNRELEASED; urgency=medium
 
   * inline: change default sort order from age to "age title" for determinism
   * img: avoid ImageMagick misinterpreting filenames containing a colon
+  * img test: set old timestamp on source file that will change, so that
+    the test will pass even if it takes less than 1 second
 
  -- Simon McVittie <smcv@debian.org>  Thu, 11 Jun 2015 08:32:35 +0100
 

t/img.t

@@ -55,6 +55,7 @@ $maybe_svg_img
 [[!img twopages.pdf size=16x pagenumber=1]]
 EOF
 );
+ok(utime(333333333, 333333333, "t/tmp/in/imgconversions.mdwn"));
 
 ok(! system("make -s ikiwiki.out"));