* cat: Unrevert splice patch
* cat: Add fifo test
* cat: Add tests for error cases
* cat: Add tests for character devices
* wc: Make sure we handle short splice writes
* cat: Fix tests for 1.40.0 compiler
* cat: Run rustfmt on test_cat.rs
* Run 'cargo +1.40.0 update'
Make at_line_start persist between printing each file. This fixes an
issue when numbering lines in the output and one of the input files
does not have a trailing newline.
