fixed some bugs in CFLAGS passing. added a specific threaded test case

* configure.in: fixed some bugs in CFLAGS passing.
* test/threads Makefile.am testThreads.c: added a specific
  threaded test case (really nasty, guaranteed).
Daniel
diff --git a/test/threads/cba.dtd b/test/threads/cba.dtd
new file mode 100644
index 0000000..71b96b4
--- /dev/null
+++ b/test/threads/cba.dtd
@@ -0,0 +1,7 @@
+<!ENTITY % c SYSTEM "http://example.org/c/c.dtd">
+%c;
+<!ENTITY % b SYSTEM "http://example.org/b/b.dtd">
+%b;
+<!ENTITY % a SYSTEM "http://example.org/a/a.dtd">
+%a;
+<!ELEMENT cba (c, b, a)>