wrapper: show the program's name in major messages
wrapper: show the program's name in major messages

Since this wrapper program is typically used in an "automatic"
(non-interactive) way, it may be helpful to the user to include the
program's name in some of the messages it prints.

Add the program's name to the following messages:

 * The "unsupported old/new OS" messages may appear by themselves
   (e.g. before the wrapper is updated to handle a new OS X release).

 * The message after the reattach_failed label will also be issued
   after any earlier message (except the old/new OS message).

 * The message for a failed exec.

Suggested-By: https://github.com/ChrisJohnsen/tmux-MacOSX-pasteboard/pull/14

bradparks/tmux-MacOSX-pasteboard,lembacon/tmux-MacOSX-pasteboard,ChrisJohnsen/tmux-MacOSX-pasteboard,tjt263/tmux-MacOSX-pasteboard