new capacity bits (#67)

tests/fixtures/xpath_injection/cpp/baseline_constant_xpath.cpp

@@ -0,0 +1,7 @@
+// Baseline: expression is a compile-time constant.  No taint reaches
+// xmlXPathEvalExpression so no XPATH_INJECTION finding fires.
+#include <libxml/xpath.h>
+
+xmlXPathObjectPtr do_lookup(xmlXPathContextPtr ctx) {
+    return xmlXPathEvalExpression((xmlChar *)"//user[@role='admin']", ctx);
+}