Expand ssh host aliases in remote urls

A common practice for using multiple accounts with a hosting service
such as GitHub is to alias the host in ~/.ssh/config and use an
alternate ssh key to authenticate as the alternate user:

	Host github.com-work
		HostName github.com
		IdentityFile ~/.ssh/id_rsa_work

By swapping in the original host name for the alias in
FugitiveRemoteUrl(), we can enable :GBrowse plugins to correctly
recognize the hosting service's domain name.

If for some reason you need the original URL without modification, pass
a true value as the third parameter:

	let url = FugitiveRemoteUrl('', bufnr(''), 1)

References https://github.com/tpope/vim-rhubarb/issues/60

plugin/fugitive.vim

@@ -122,7 +122,7 @@ function! FugitiveConfigGetAll(name, ...) abort
 endfunction
 
 function! FugitiveRemoteUrl(...) abort
-  return fugitive#RemoteUrl(a:0 ? a:1 : '', FugitiveGitDir(a:0 > 1 ? a:2 : -1))
+  return fugitive#RemoteUrl(a:0 ? a:1 : '', FugitiveGitDir(a:0 > 1 ? a:2 : -1), a:0 > 2 ? a:3 : 0)
 endfunction
 
 function! FugitiveHead(...) abort