patch 7.4.1310

Problem:    Jobs don't open a channel.
Solution:   Create pipes and add them to the channel.  Add ch_logfile().
            Only Unix for now.

src/testdir/test_channel_pipe.py

@@ -0,0 +1,24 @@
+#!/usr/bin/python
+#
+# Server that will communicate over stdin/stderr
+#
+# This requires Python 2.6 or later.
+
+from __future__ import print_function
+import sys
+
+if __name__ == "__main__":
+
+    if len(sys.argv) > 1:
+        print(sys.argv[1])
+
+    while True:
+        typed = sys.stdin.readline()
+        if typed.startswith("quit"):
+            print("Goodbye!")
+            sys.stdout.flush()
+            break
+        if typed.startswith("echo"):
+            print(typed[5:-1])
+            sys.stdout.flush()
+