Enhance "check-ignore" (1.8.2 update) to work more like "check-attr"
over bidi-pipes.
* as/check-ignore:
t0008: use named pipe (FIFO) to test check-ignore streaming
Documentation: add caveats about I/O buffering for check-{attr,ignore}
check-ignore: allow incremental streaming of queries via --stdin
check-ignore: move setup into cmd_check_ignore()
check-ignore: add -n / --non-matching option
t0008: remove duplicated test fixture data