Update 'validate=' parameter documentation to make clear that the command

passed via this paramter is not passed via shell and so all shell features
will not work.

library/files/copy

@@ -73,6 +73,7 @@ options:
     description:
       - The validation command to run before copying into place.  The path to the file to
         validate is passed in via '%s' which must be present as in the visudo example below.
+        The command is passed securely so shell features like expansion and pipes won't work.
     required: false
     default: ""
     version_added: "1.2"

library/files/lineinfile

@@ -110,7 +110,8 @@ options:
   validate:
      required: false
      description:
-       - validation to run before copying into place
+       - validation to run before copying into place. The command is passed 
+         securely so shell features like expansion and pipes won't work.
      required: false
      default: None
      version_added: "1.4"

library/files/template

@@ -40,7 +40,8 @@ options:
     default: "no"
   validate:
     description:
-      - validation to run before copying into place
+      - validation to run before copying into place. The command is passed 
+        securely so shell features like expansion and pipes won't work.
     required: false
     default: ""
     version_added: "1.2"