tests: add a test for the latest dumpio fix

* tests/dumpio.expected: New file.
* tests/unix-pair-send-recv.c: New file.
* tests/dumpio.test: New test.
* tests/Makefile.am (check_PROGRAMS): Add unix-pair-send-recv.
(TESTS): Add dumpio.test.
(EXTRA_DIST): Add dumpio.expected.
* tests/.gitignore: Add unix-pair-send-recv.
diff --git a/tests/.gitignore b/tests/.gitignore
index 1510bc9..c96ee1f 100644
--- a/tests/.gitignore
+++ b/tests/.gitignore
@@ -20,6 +20,7 @@
 uid16
 uid32
 uio
+unix-pair-send-recv
 *.log
 *.log.*
 *.o