Honor SOURCE_DATE_EPOCH when exporting configuration date.
Autoconf-level patch submitted upstream on Wed Apr 13 17:03:23 UTC 2016

--- a/configure
+++ b/configure
@@ -27737,7 +28573,14 @@
 
 
 ## Configuration date
- CONFIG_DATE="`date`"
+ CONFIG_DATE="`date -u`"
+if test -n "$SOURCE_DATE_EPOCH"; then
+  CONFIG_DATE=`date -u -d "@$SOURCE_DATE_EPOCH" 2>/dev/null \
+               || date -u -r "$SOURCE_DATE_EPOCH" 2>/dev/null`
+  if test -z "$CONFIG_DATE"; then
+    as_fn_error $? "malformed SOURCE_DATE_EPOCH" "$LINENO" 5
+  fi
+fi
 
 ## User doing the configuration
  CONFIG_USER="`whoami`@`hostname`"
put type='hidden' name='id' value='71e1d0a4373f6cc5cd99e1400fb87d64d97c370f'/><select name='h' onchange='this.form.submit();'>
<option value='koszko' selected='selected'>koszko</option>
<option value='koszko-scripts'>koszko-scripts</option>
</select> <input type='submit' value='switch'/></form></td></tr>
<tr><td class='sub'>Wojtek's customized Guix</td><td class='sub right'></td></tr></table>
<table class='tabs'><tr><td>
<a href='/guix/about/'>about</a><a href='/guix/'>summary</a><a href='/guix/refs/?id=71e1d0a4373f6cc5cd99e1400fb87d64d97c370f'>refs</a><a class='active' href='/guix/log/gnu/packages/tcl.scm'>log</a><a href='/guix/tree/gnu/packages/tcl.scm?id=71e1d0a4373f6cc5cd99e1400fb87d64d97c370f'>tree</a><a href='/guix/commit/gnu/packages/tcl.scm?id=71e1d0a4373f6cc5cd99e1400fb87d64d97c370f'>commit</a><a href='/guix/diff/gnu/packages/tcl.scm?id=71e1d0a4373f6cc5cd99e1400fb87d64d97c370f'>diff</a></td><td class='form'><form class='right' method='get' action='/guix/log/gnu/packages/tcl.scm'>
<input type='hidden' name='id' value='71e1d0a4373f6cc5cd99e1400fb87d64d97c370f'/><select name='qt'>
<option value='grep'>log msg</option>
<option value='author'>author</option>
<option value='committer'>committer</option>
<option value='range'>range</option>
</select>
<input class='txt' type='search' size='10' name='q' value=''/>
<input type='submit' value='search'/>
</form>
</td></tr></table>
<div class='path'>path: <a href='/guix/log/?id=71e1d0a4373f6cc5cd99e1400fb87d64d97c370f'>root</a>/<a href='/guix/log/gnu?id=71e1d0a4373f6cc5cd99e1400fb87d64d97c370f'>gnu</a>/<a href='/guix/log/gnu/packages?id=71e1d0a4373f6cc5cd99e1400fb87d64d97c370f'>packages</a>/<a href='/guix/log/gnu/packages/tcl.scm?id=71e1d0a4373f6cc5cd99e1400fb87d64d97c370f'>tcl.scm</a></div><div class='content'><table class='list nowrap'><tr class='nohover'><th class='left'>Age</th><th class='left'>Commit message (<a href='/guix/log/gnu/packages/tcl.scm?id=71e1d0a4373f6cc5cd99e1400fb87d64d97c370f&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>