Add ACLOCAL_AMFLAGS

Original commit message from CVS:
Add ACLOCAL_AMFLAGS
diff --git a/Makefile.am b/Makefile.am
index c6d6c5e..c3c43e5 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -24,6 +24,8 @@
 gst-element-check-@GST_MAJORMINOR@.m4: gst-element-check.m4
 	cp $(srcdir)/gst-element-check.m4 gst-element-check-@GST_MAJORMINOR@.m4
 
+ACLOCAL_AMFLAGS = -I common/m4
+
 aclocaldir = $(datadir)/aclocal
 aclocal_DATA = gst-element-check-@GST_MAJORMINOR@.m4