fixed type bug

Hi there,

I'm having this error message:

```
Error: Could not retrieve catalog from remote server: Error 400 on SERVER: Evaluation Error: Error creating type specialization of an Apache::listen-Type, Cannot use Fixnum where String is expected at /etc/puppet/environments/myenv/modules/apache/manifests/vhost.pp:354:33 on node puppet.mydomain.com
Warning: Not using cache on failed catalog
Error: Could not retrieve catalog; skipping run
```

my manifest says:

```puppet
  package { 'nagios3': ensure => installed }

  class { 'apache':
    mpm_module    => 'prefork',
    default_mods  => false,
    default_vhost => false
  }

  include apache::mod::rewrite

  include apache::mod::php

  apache::vhost { 'nagios.mydomain.com':
    port    => '80',
    docroot => '/usr/share/nagios3/htdocs',
  } -> exec { 'enable apache nagios conf':
    command => '/bin/bash -c "a2enconf nagios3"',
    path    => ['/usr/sbin/', '/usr/bin/'],
    unless  => "/bin/readlink -e /etc/apache2/conf-enabled/nagios3.conf",
  }
```


Maybe a correct type check is more elegant :)
but this works for me.


cheers!