fs: extend reported types in  uv_fs_readdir_next

Support all possible types on Unix, and files, directories and links on
Windows. Some systems (hello SunOS!) don't have the d_type field on struct
dirent, so mark them as UV_DIRENT_UNKNOWN.
unix: fix colliding flag value

Fixes #1425
unix: read on stream even when UV__POLLHUP set.

This fixes a SmartOS specific issue that happens when reading from
a stream that is the reading end of a pipe that has been closed by
the parent process.

In this case, a UV__POLLHUP event would be set on the stream and would
prevent the event loop from closing it. As a result, the event loop
would think there are stil handles open, and leave the process
hanging.

Fixes #1419.