Call the imlib2-conf variable that are set by ac_cv_path_IMLIB2_CONFIG
with the absolute path because the imlib2-config file is not covered
by the PATH variable.
This is important for cross compiler that need to get the staging settings
instead of the host settings.

Signed-off-by: Carsten Schoenert <c.schoenert@gmail.com>

--- directfb-1.6.3/configure.orig	2013-03-31 13:18:22.837560379 +0200
+++ directfb-1.6.3/configure	2013-03-31 13:23:40.177541099 +0200
@@ -19816,8 +19816,8 @@ fi
 $as_echo "$as_me: WARNING: *** Imlib2 library not found, building without Imlib2 support ***" >&2;}
     imlib2="no"
   else
-    IMLIB2_CFLAGS=`imlib2-config --cflags`
-    IMLIB2_LIBS=`imlib2-config --libs`
+    IMLIB2_CFLAGS=`$IMLIB2_CONFIG --cflags`
+    IMLIB2_LIBS=`$IMLIB2_CONFIG --libs`
     imlib2="yes"
   fi
 fi