For push map, never push to fetch remote

There are legitimate reasons to push to the fetch remote, but making it
possible from the push map makes it too easy to do by default.

autoload/fugitive.vim

@@ -5158,11 +5158,12 @@ function! s:DoToggleHelpHeader(value) abort
 endfunction
 
 function! s:DoStagePushHeader(value) abort
-  let remote = matchstr(a:value, '\zs[^/]\+\ze/')
+  let stat = get(b:, 'fugitive_status', {})
-  if empty(remote)
+  let remote = get(stat, 'push_remote', '')
-    let remote = '.'
+  let branch = substitute(get(stat, 'push', ''), '^ref/heads/', '', '')
+  if empty(remote) || empty(branch)
+    return
   endif
-  let branch = matchstr(a:value, '\%([^/]\+/\)\=\zs\S\+')
   call feedkeys(':Git push ' . remote . ' ' . branch)
 endfunction
 
@@ -5171,15 +5172,13 @@ function! s:DoTogglePushHeader(value) abort
 endfunction
 
 function! s:DoStageUnpushedHeading(heading) abort
-  let remote = matchstr(a:heading, 'to \zs[^/]\+\ze/')
+  let stat = get(b:, 'fugitive_status', {})
-  if empty(remote)
+  let remote = get(stat, 'push_remote', '')
-    let remote = '.'
+  let push = get(stat, 'push', '')
-  endif
+  if empty(remote) || empty(push)
-  let branch = matchstr(a:heading, 'to \%([^/]\+/\)\=\zs\S\+')
-  if branch ==# '*'
     return
   endif
-  call feedkeys(':Git push ' . remote . ' ' . '@:' . 'refs/heads/' . branch)
+  call feedkeys(':Git push ' . remote . ' ' . '@:' . push)
 endfunction
 
 function! s:DoToggleUnpushedHeading(heading) abort
@@ -5187,15 +5186,13 @@ function! s:DoToggleUnpushedHeading(heading) abort
 endfunction
 
 function! s:DoStageUnpushed(record) abort
-  let remote = matchstr(a:record.heading, 'to \zs[^/]\+\ze/')
+  let stat = get(b:, 'fugitive_status', {})
-  if empty(remote)
+  let remote = get(stat, 'push_remote', '')
-    let remote = '.'
+  let push = get(stat, 'push', '')
-  endif
+  if empty(remote) || empty(push)
-  let branch = matchstr(a:record.heading, 'to \%([^/]\+/\)\=\zs\S\+')
-  if branch ==# '*'
     return
   endif
-  call feedkeys(':Git push ' . remote . ' ' . a:record.commit . ':' . 'refs/heads/' . branch)
+  call feedkeys(':Git push ' . remote . ' ' . a:record.commit . ':' . push)
 endfunction
 
 function! s:DoToggleUnpushed(record) abort