Accept --autoremove as alias for --auto-remove

I probably missed that when I did the usability work. But better
late than never.

apt-private/private-cmndline.cc

@@ -189,6 +189,7 @@ static bool addArgumentsAPTGet(std::vector<CommandLine::Args> &Args, char const
       addArg('f', "fix-broken", "APT::Get::Fix-Broken", 0);
       addArg(0, "purge", "APT::Get::Purge", 0);
       addArg('V',"verbose-versions","APT::Get::Show-Versions",0);
+      addArg(0, "autoremove", "APT::Get::AutomaticRemove", 0);
       addArg(0, "auto-remove", "APT::Get::AutomaticRemove", 0);
       addArg(0, "reinstall", "APT::Get::ReInstall", 0);
       addArg(0, "solver", "APT::Solver", CommandLine::HasArg);

doc/apt-get.8.xml

@@ -522,7 +522,7 @@
      Configuration Item: <literal>APT::Get::Remove</literal>.</para></listitem>
      </varlistentry>
 
-     <varlistentry><term><option>--auto-remove</option></term>
+     <varlistentry><term><option>--auto-remove</option></term><term><option>--autoremove</option></term>
      <listitem><para>If the command is either <literal>install</literal> or <literal>remove</literal>,
      then this option acts like running the <literal>autoremove</literal> command, removing unused
      dependency packages. Configuration Item: <literal>APT::Get::AutomaticRemove</literal>.