Infrastructure for extracting syntax tests in separate test files.

test/libsolidity/syntaxTests/double_stateVariable_declaration.sol

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+contract test {
+	uint256 variable;
+	uint128 variable;
+}
+// ----
+// DeclarationError: Identifier already declared.

test/libsolidity/syntaxTests/double_variable_declaration.sol

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+contract test {
+	function f() pure public {
+		uint256 x;
+		if (true) { uint256 x; }
+	}
+}
+// ----
+// DeclarationError: Identifier already declared.

test/libsolidity/syntaxTests/double_variable_declaration_050.sol

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+pragma experimental "v0.5.0";
+contract test {
+	function f() pure public {
+		uint256 x;
+		if (true) { uint256 x; }
+	}
+}
+// ----
+// Warning: This declaration shadows an existing declaration.
+// Warning: Unused local variable.
+// Warning: Unused local variable.

test/libsolidity/syntaxTests/smoke_test.sol

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+contract test {
+	uint256 stateVariable1;
+	function fun(uint256 arg1) public { uint256 y; y = arg1; }
+}
+// ----
+// Warning: Function state mutability can be restricted to pure