stdio, stdout, stderr won't work in shared libraries

This is a result of the hack used to fix issue #4. We have to add the code added to dmain2.d to some runtime function which get's called when the shared library is loaded. A better fix is to detect if druntime is built as a shared library and do not use the workaround in that case.

Once shared libraries are working, we should probably just drop support for static executables.
