rework select_folder error handling (thanks @flub and @link2xt for helping along)

src/error.rs

@@ -54,6 +54,12 @@ pub enum Error {
     ImapInTeardown,
     #[fail(display = "No IMAP Connection established")]
     ImapNoConnection,
+    /*
+    #[fail(display = "IMAP Connection lost: {:?}", _0)]
+    ImapConnectionLost(String),
+    #[fail(display = "Failed to obtain Imap Session")]
+    CouldNotObtainImapSession,
+    */
 }
 
 pub type Result<T> = std::result::Result<T, Error>;