Reformat command postfix to (PID/label)

For example, instead of (tmux/12345), show (12345/Running).

This is updated in all cases where a postfix is added to command in
messages to the user, including the quickfix title.

For updating quickfix lists, the title up to the '/' character in the
postfix is used.

autoload/dispatch.vim

@@ -371,15 +371,12 @@ endfunction
 
 function! s:postfix(request) abort
   let pid = dispatch#pid(a:request)
-  return '(' . a:request.handler.'/'.(!empty(pid) ? pid : '?') . ')'
+  let label = get(a:request, 'label', 'Running')
+  return '(' . (!empty(pid) ? pid : '?') . '/' . label . ')'
 endfunction
 
-function! s:status_label(request) abort
-    let label = get(a:request, 'label', '') . get(a:request, 'status', '')
-    if !empty(label)
-        return '(' . label . ')'
-    endif
-    return ''
+function! s:quickfix_title(request) abort
+    return ':Dispatch '.dispatch#escape(a:request.expanded) . ' ' . s:postfix(a:request)
 endfunction
 
 function! s:echo_truncated(left, right) abort
@@ -1219,24 +1216,22 @@ function! dispatch#complete(file, ...) abort
     endif
     if has_key(request, 'aborted')
       echohl DispatchAbortedMsg
-      let label = 'Aborted:'
+      let request.label = 'Aborted'
     elseif status > 0
       echohl DispatchFailureMsg
-      let label = 'Failure:'
+      let request.label = 'Failure'
     elseif status == 0
       echohl DispatchSuccessMsg
-      let label = 'Success:'
+      let request.label = 'Success'
     else
       echohl DispatchCompleteMsg
-      let label = 'Complete:'
+      let request.label = 'Complete'
     endif
-    let request.label = label
-    let request.status = status
     if !request.background && !get(request, 'aborted')
       call s:cwindow(request, 0, status, '', 'make')
       redraw!
     endif
-    call s:echo_truncated(label . '!', request.expanded . ' ' . s:postfix(request))
+    call s:echo_truncated('!', request.expanded . ' ' . s:postfix(request))
     echohl NONE
     if !a:0
       checktime
@@ -1316,18 +1311,18 @@ function! s:cgetfile(request, event, ...) abort
       let &l:efm = request.format
     endif
     let &l:makeprg = dispatch#escape(request.expanded)
-    let title = ':Dispatch '.dispatch#escape(request.expanded) . ' ' . s:postfix(request)
     if len(a:event)
       exe 'silent doautocmd QuickFixCmdPre' a:event
     endif
-    if exists(':chistory') && stridx(get(getqflist({'title': 1}), 'title', ''), title) >= 0
+    let title = s:quickfix_title(request)
+    let title_to_match = title[:strridx(title, '/')]
+    if exists(':chistory') && stridx(get(getqflist({'title': 1}), 'title', ''), title_to_match) >= 0
       call setqflist([], 'r')
       execute 'noautocmd caddfile' dispatch#fnameescape(request.file)
     else
       execute 'noautocmd cgetfile' dispatch#fnameescape(request.file)
     endif
     if exists(':chistory')
-      let title .= ' ' . s:status_label(request)
       call setqflist([], 'r', {'title': title})
     endif
     if len(a:event)