Fixed use of libraries.

libsolidity/CompilerStack.cpp

@@ -264,7 +264,7 @@ void CompilerStack::reset(bool _keepSources)
 	{
 		m_sources.clear();
 		if (m_addStandardSources)
-			addSources(StandardSources);
+			addSources(StandardSources, true);
 	}
 	m_globalContext.reset();
 	m_sourceOrder.clear();

libsolidity/CompilerStack.h

@@ -140,7 +140,7 @@ private:
 		std::shared_ptr<SourceUnit> ast;
 		std::string interface;
 		bool isLibrary = false;
-		void reset() { scanner.reset(); ast.reset(); interface.clear(); isLibrary = false;}
+		void reset() { scanner.reset(); ast.reset(); interface.clear(); }
 	};
 
 	struct Contract