tests: add swap.test

* tests/swap.c: New file.
* tests/swap.test: New test.
* tests/.gitignore: Add swap.
* tests/Makefile.am (check_PROGRAMS): Likewise.
(DECODER_TESTS): Add swap.test.
diff --git a/tests/.gitignore b/tests/.gitignore
index 9ebab08..c488409 100644
--- a/tests/.gitignore
+++ b/tests/.gitignore
@@ -137,6 +137,7 @@
 stat
 stat64
 statfs
+swap
 sync_file_range
 sync_file_range2
 sysinfo