Added test program [#MOBMET-3953].

dbms/src/Core/tests/string_ref_hash.cpp

+#include <DB/IO/ReadBufferFromFileDescriptor.h>
+#include <DB/IO/WriteBufferFromFileDescriptor.h>
+#include <DB/IO/WriteBufferFromString.h>
+#include <DB/IO/Operators.h>
+#include <DB/Core/StringRef.h>
+
+
+/** Calculates StringRefHash from stdin. For debugging.
+  */
+
+int main(int argc, char ** argv)
+{
+	using namespace DB;
+
+	ReadBufferFromFileDescriptor in(STDIN_FILENO);
+	WriteBufferFromFileDescriptor out(STDOUT_FILENO);
+
+	String s;
+	readStringUntilEOF(s, in);
+	out << StringRefHash()(s) << '\n';
+
+	return 0;
+}