swift234

Teach module lookup to look first in the directory where the importing
module is located, and then fall back to the current directory if
nothing was found there. This allows us to run the Swift regression
tests from a directory other than "test" (e.g., in the build
directory, as is currently needed by CMake).

The implementation itself is a temporary hack that will eventually
need to be replaced with a proper virtual file system + module
manager.


Swift SVN r405