Fix problem with switching between Rust buffers.

This was also causing trouble if one didn't have delimitMate installed.

Author: chris-morgan

src/etc/vim/ftplugin/rust.vim

@@ -40,4 +40,4 @@ if exists("g:loaded_delimitMate")
 	let b:delimitMate_excluded_regions = delimitMate#Get("excluded_regions") . ',rustLifetimeCandidate,rustGenericLifetimeCandidate'
 endif
 
-let b:undo_ftplugin = "setlocal formatoptions< comments< commentstring< includeexpr< suffixesadd< | if exists('b:rust_original_delimitMate_excluded_regions') | let b:delimitMate_excluded_regions = b:rust_original_delimitMate_excluded_regions | unlet b:rust_original_delimitMate_excluded_regions | else | unlet b:delimitMate_excluded_regions | endif"
+let b:undo_ftplugin = "setlocal formatoptions< comments< commentstring< includeexpr< suffixesadd< | if exists('b:rust_original_delimitMate_excluded_regions') | let b:delimitMate_excluded_regions = b:rust_original_delimitMate_excluded_regions | unlet b:rust_original_delimitMate_excluded_regions | elseif exists('b:delimitMate_excluded_regions') | unlet b:delimitMate_excluded_regions | endif"