[rubygems/rubygems] Don't use util_installer for user install

It is not nice to require install directory to be always specified,
while this option is later ignored for user installed gems.

Actually, the next step will be to remove `check_install_dir` check and
let the install dir override the user install.

rubygems/rubygems@beb79e929f

test/rubygems/installer_test_case.rb

@@ -111,7 +111,7 @@ def util_make_exec(spec = @spec, shebang = "#!/usr/bin/ruby", bindir = "bin")
 
   def setup_base_installer(force = true)
     @gem = setup_base_gem
-    util_installer @spec, @gemhome, false, force
+    util_installer @spec, @gemhome, force
   end
 
   ##
@@ -163,7 +163,7 @@ def setup_base_user_installer
 
     @user_gem = @user_spec.cache_file
 
-    util_installer @user_spec, Gem.user_dir, :user
+    Gem::Installer.at @user_gem, :user_install => true
   end
 
   ##
@@ -219,13 +219,11 @@ def util_setup_gem(ui = @ui, force = true)
   end
 
   ##
-  # Creates an installer for +spec+ that will install into +gem_home+.  If
-  # +user+ is true a user-install will be performed.
+  # Creates an installer for +spec+ that will install into +gem_home+.
 
-  def util_installer(spec, gem_home, user=false, force=true)
+  def util_installer(spec, gem_home, force=true)
     Gem::Installer.at(spec.cache_file,
                        :install_dir => gem_home,
-                       :user_install => user,
                        :force => force)
   end