Added reply quoting to the GUI.

Ideally this should quote only the selected text if any text is selected
in the message viewer when the user presses reply.  At least that's how
my email client works.

I assume Go initalizes the two local varialbes I eliminated to zero,
but I thought it looked cleaner to initalize them explicitly and
and set them if inReplyTo is set.  <shrug>
Don't try to read from terminal after error.

Previously an EOF from the terminal would cause one of the goroutines to
busy-loop until another recorded the error and exited the process.
Touch up reply-quoting patch for GUI.

Move indentForReply, which is now common between cli and gui, into
client.go
Merge branch 'master' of github.com:agl/pond
Merge branch 'burdges-master'