trivial change (changed CHECK_CONTEXT to CHECK_CTXT on a couple of lines)

* xpath.c: trivial change (changed CHECK_CONTEXT to CHECK_CTXT
  on a couple of lines)
* gentest.py, testapi.c: enhanced to reduce compilation warnings
diff --git a/xpath.c b/xpath.c
index fad8c26..8afbb34 100644
--- a/xpath.c
+++ b/xpath.c
@@ -3931,9 +3931,13 @@
 
 #define CHECK_CTXT(ctxt)						\
     if (ctxt == NULL) { 						\
-        xmlGenericError(xmlGenericErrorContext,				\
-		"%s:%d Internal error: ctxt == NULL\n",			\
-	        __FILE__, __LINE__);					\
+	__xmlRaiseError(NULL, NULL, NULL,				\
+		NULL, NULL, XML_FROM_XPATH,				\
+		XML_ERR_INTERNAL_ERROR, XML_ERR_FATAL,			\
+		__FILE__, __LINE__,					\
+		NULL, NULL, NULL, 0, 0,					\
+		"NULL context pointer\n");				\
+	return(NULL);							\
     }									\
 
 
@@ -11105,12 +11109,12 @@
     static int reentance = 0;
 #endif
 
-    if ((comp == NULL) || (ctx == NULL))
+    CHECK_CTXT(ctx)
+
+    if (comp == NULL)
 	return(NULL);
     xmlXPathInit();
 
-    CHECK_CONTEXT(ctx)
-
 #ifndef LIBXML_THREAD_ENABLED
     reentance++;
     if (reentance > 1)
@@ -11194,9 +11198,9 @@
     xmlXPathObjectPtr res, tmp, init = NULL;
     int stack = 0;
 
-    xmlXPathInit();
+    CHECK_CTXT(ctx)
 
-    CHECK_CONTEXT(ctx)
+    xmlXPathInit();
 
     ctxt = xmlXPathNewParserContext(str, ctx);
     xmlXPathEvalExpr(ctxt);
@@ -11250,9 +11254,9 @@
     xmlXPathObjectPtr res, tmp;
     int stack = 0;
 
-    xmlXPathInit();
+    CHECK_CTXT(ctxt)
 
-    CHECK_CONTEXT(ctxt)
+    xmlXPathInit();
 
     pctxt = xmlXPathNewParserContext(str, ctxt);
     xmlXPathEvalExpr(pctxt);