Remove "using namespace" from header and move Instruction to dev::eth.

libsolidity/codegen/ExpressionCompiler.cpp

@@ -39,11 +39,10 @@
 
 using namespace std;
 using namespace langutil;
+using namespace dev;
+using namespace dev::eth;
+using namespace dev::solidity;
 
-namespace dev
-{
-namespace solidity
-{
 
 void ExpressionCompiler::compile(Expression const& _expression)
 {
@@ -2269,6 +2268,3 @@ CompilerUtils ExpressionCompiler::utils()
 {
 	return CompilerUtils(m_context);
 }
-
-}
-}