issue7213: Open the pipes used by subprocesses with the FD_CLOEXEC flag from

the C code, using pipe2() when available.  Adds unittests for close_fds and
cloexec behaviors.

Lib/test/subprocessdata/qcat.py

@@ -0,0 +1,7 @@
+"""When ran as a script, simulates cat with no arguments."""
+
+import sys
+
+if __name__ == "__main__":
+    for line in sys.stdin:
+        sys.stdout.write(line)