Bug 12930: Web installer does not show login errors

Implemented invalid_username_or_password template
variable being handed to Auth.tt. Removed indentation
changes and modification to return value of checkpw

Test plan:
See comment #2

Alternative test plan:
- Clear session cookies or close / open your browser
- Go to  [MY SERVER]/cgi-bin/koha/installer/install.pl
- Verify that message appears if wrong username/pw provided
- Verify that you can log in with databas administrator account

Tested with alternative test plan, works as expected. Title and
description in commit message adapted.
Signed-off-by: Marc Véron <veron@veron.ch>

Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>

Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
(cherry picked from commit 87eb80136d)
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>

C4/InstallAuth.pm

@@ -379,6 +379,10 @@ sub checkauth {
     $template->param( login => 1 );
     $template->param( loginprompt => 1 ) unless $info{'nopermission'};
 
+    if ($info{'invalid_username_or_password'} == 1) {
+                $template->param( 'invalid_username_or_password' => $info{'invalid_username_or_password'});
+    }
+
     $template->param( \%info );
     $cookie = $query->cookie(
         -name    => 'CGISESSID',