Fix OpenCV detection code

--- ./config.m4
+++ ./config.m4
@@ -28,7 +28,7 @@ if test "$PHP_FACEDETECT" != "no"; then
   AC_CHECK_HEADER([opencv/cvver.h], [], AC_MSG_ERROR('opencv/cvver.h' header not found))
   AC_CHECK_HEADER([opencv/highgui.h], [], AC_MSG_ERROR('opencv/highgui.h' header not found))
 
-  PHP_CHECK_LIBRARY(cv, cvLoad,
+  PHP_CHECK_LIBRARY(cxcore, cvLoad,
   [
     PHP_ADD_LIBRARY_WITH_PATH(cv, $FACEDETECT_DIR/lib, FACEDETECT_SHARED_LIBADD)
     PHP_ADD_LIBRARY_WITH_PATH(cvaux, $FACEDETECT_DIR/lib, FACEDETECT_SHARED_LIBADD)