fixed problem with 'minimal library' compilation (LIBXML_PATTERN_ENABLED

* gentest.py, testapi.c: fixed problem with 'minimal library'
  compilation (LIBXML_PATTERN_ENABLED not properly checked) reported
  by Greg Morgan
diff --git a/gentest.py b/gentest.py
index 234685c..e4ede36 100755
--- a/gentest.py
+++ b/gentest.py
@@ -45,6 +45,7 @@
     "xmlsave" : "LIBXML_OUTPUT_ENABLED",
     "DOCBparser" : "LIBXML_DOCB_ENABLED",
     "xmlmodule" : "LIBXML_MODULES_ENABLED",
+    "pattern" : "LIBXML_PATTERN_ENABLED",
 }
 
 #