tools: disable xend build by default

Add big warnings to configure, xend initscript and xm.

The big xm warning is displayed once (per boot, or per tmpreaper clean),
afterwards a single line warning is displayed.

Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
Acked-by: Ian Jackson <ian.jackson@eu.citrix.com>

tools/python/xen/xm/xm

@@ -1,7 +1,20 @@
 #!/usr/bin/env python
 #  -*- mode: python; -*-
-import sys
+import sys, os.path
 
 from xen.xm import main
 
+print("WARNING: xend/xm is deprecated.")
+
+if not os.path.exists("/tmp/xm-deprecation-long-warning"):
+    print("""
+xend is deprecated and scheduled for removal. Please migrate to another
+toolstack ASAP.
+
+See http://wiki.xen.org/wiki/Choice_of_Toolstacks for information on
+other alternatives, including xl which is designed to be a drop in
+replacement for xm (http://wiki.xen.org/wiki/XL).
+""")
+    open("/tmp/xm-deprecation-long-warning", "w").close()
+
 main.main(sys.argv)