[gtk-doc] configure: more tweaks for the macosx date command

[Stefan Kost <stefkost src gnome org>]

commit 31936ea8c47433eb73c3441fc73ec158f32f41f4
Author: Stefan Sauer <ensonic users sf net>
Date:   Wed Feb 19 19:22:45 2014 +0100

    configure: more tweaks for the macosx date command
    
    Fixes #671519 again.

 configure.ac |    4 +++-
 1 files changed, 3 insertions(+), 1 deletions(-)
---
diff --git a/configure.ac b/configure.ac
index 3d1b92f..68dc0a6 100644
--- a/configure.ac
+++ b/configure.ac
@@ -210,8 +210,10 @@ fi
 AC_SUBST(TRACE)
 
 dnl check what date format we can use for the makefile tracing in tests
+dnl this is mostly to detect the date command on macosx that is quite cripled
+dnl  and broken too
 AC_MSG_CHECKING(whether date can output nanoseconds)
-date +%s.%N | grep -q '%N'
+date +%s.%N | grep -q 'N'
 if test "$?" == "1"; then
   TS_FMT="+%s.%N"
   ELAPSED_FMT="+%H:%M:%S.%N"