This means that `rg pat < file` won't do the expected thing and search
`fil`. Instead, it will recursively search the current directory for `pat`.
This isn't ideal, but is better than the previous behavior, which was to
wait for stdin when running `rg pat`, given the appearance of hanging
forever. The former is an important use case, but the latter is the
*central* use case of ripgrep, so we should make that work.
`rg` can still be used to search stdin on Windows, it just needs to be
done explicitly. e.g., `rg pat - < file` will search for `pat` in `file`.
Fixes#19
If no paths are given to ripgrep, only read from stdin if it's a file or
a FIFO. In particular, if something like `rg foo < /dev/null` is used,
then don't try to read from stdin.
Fixes#35, #81
