Properly export symbols from aliased imports.

test/libsolidity/syntaxTests/imports/alias_import_not_forwarded.sol

@@ -0,0 +1,8 @@
+==== Source: dummy ====
+contract Dummy { string public constant FOO = "FOO"; }
+==== Source: hasAlias ====
+import {Dummy as AliasedDummy} from "dummy";
+==== Source: Main ====
+import {AliasedDummy} from "hasAlias";
+contract TestAlias is AliasedDummy {}
+// ----