Support multiple sources for syntax tests.

test/libsolidity/syntaxTests/multiSource/error_in_first.sol

@@ -0,0 +1,10 @@
+==== Source: A ====
+contract A {
+	function g() public { x; }
+}
+==== Source: B ====
+contract B {
+	function f() public { }
+}
+// ----
+// DeclarationError: (A:36-37): Undeclared identifier.

test/libsolidity/syntaxTests/multiSource/import.sol

@@ -0,0 +1,12 @@
+==== Source: A ====
+contract A {
+	function g(uint256 x) public view returns(uint256) { return x; }
+}
+==== Source: B ====
+import "A";
+contract B is A {
+	function f(uint256 x) public view returns(uint256) { return x; }
+}
+// ----
+// Warning: (A:14-78): Function state mutability can be restricted to pure
+// Warning: (B:31-95): Function state mutability can be restricted to pure

test/libsolidity/syntaxTests/multiSource/import_not_found.sol

@@ -0,0 +1,5 @@
+==== Source: a ====
+import "b";
+contract C {}
+// ----
+// ParserError: (a:0-11): Source "b" not found: File not supplied initially.

test/libsolidity/syntaxTests/multiSource/no_import.sol

@@ -0,0 +1,10 @@
+==== Source: A ====
+contract A {
+	function g(uint256 x) public view returns(uint256) { return x; }
+}
+==== Source: B ====
+contract B is A {
+	function f(uint256 x) public view returns(uint256) { return x; }
+}
+// ----
+// DeclarationError: (B:14-15): Identifier not found or not unique.

test/libsolidity/syntaxTests/multiSource/one_source.sol

@@ -0,0 +1,7 @@
+==== Source: SourceName ====
+contract A {
+	uint256 x;
+	function f() public pure { x = 42; }
+}
+// ----
+// TypeError: (SourceName:53-54): Function declared as pure, but this expression (potentially) modifies the state and thus requires non-payable (the default) or payable.

test/libsolidity/syntaxTests/multiSource/warning_in_both.sol

@@ -0,0 +1,11 @@
+==== Source: A ====
+contract A {
+	function g(uint256 x) public view returns(uint256) { return x; }
+}
+==== Source: B ====
+contract B {
+	function f(uint256 x) public view returns(uint256) { return x; }
+}
+// ----
+// Warning: (A:14-78): Function state mutability can be restricted to pure
+// Warning: (B:14-78): Function state mutability can be restricted to pure