Optionally use fs.lstat to read symlinks

Currently if a watched directory has symlinks, supervisor reports an error on `fs.stat()` of the symlink.
It could `fs.lstat()` the files instead, which should cause it to read the symlink itself (not the linked file). This PR adds an `--lstat` flag which simply changes the command from `stat` to `lstat`. It's probably only half the solution to symlinks -- it should really `fs.readlink()` the symlink (if `file.isSymbolicLink()`), and then watched the read directory -- but I'm not sure how to best do that generically. So this is half a solution to a situation many people might have, interested in feedback on how to flesh it out.

Thanks!