Clear GPGOptions/GPGRecipients autocommands on BufUnload

The BufHidden autocommand will have already called the respective Finish
function.  Clearing the autocommands during BufUnload ensures they don't
inadvertently run when Vim is shutting down.

Closes #104

autoload/gnupg.vim

@@ -685,7 +685,8 @@ function gnupg#edit_recipients()
     augroup GPGRecipients
       au! * <buffer>
       " add a autocommand to regenerate the recipients after a write
-      autocmd BufHidden,BufUnload,BufWriteCmd <buffer> call s:GPGFinishRecipientsBuffer()
+      autocmd BufHidden,BufWriteCmd <buffer> call s:GPGFinishRecipientsBuffer()
+      autocmd BufUnload <buffer> exe 'au! GPGRecipients * <buffer='. expand('<abuf>') .'>'
     augroup END
 
     " put some comments to the scratch buffer
@@ -861,7 +862,8 @@ function gnupg#edit_options()
     augroup GPGOptions
       au! * <buffer>
       " add a autocommand to regenerate the options after a write
-      autocmd BufHidden,BufUnload,BufWriteCmd <buffer> call s:GPGFinishOptionsBuffer()
+      autocmd BufHidden,BufWriteCmd <buffer> call s:GPGFinishOptionsBuffer()
+      autocmd BufUnload <buffer> exe 'au! GPGOptions * <buffer='. expand('<abuf>') .'>'
     augroup END
 
     " put some comments to the scratch buffer