update freebsd default version to 2.4

FreeBSD updated its default Apache version to 2.4 in July.
```
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
                      H E A D S - U P
2014-07-13:
  The default version was changed from www/apache22 to www/apache24,
  pre-build apache modules will also reflect this!

  In case ports are build by yourself and apache22 is required
  use the following command to keep apache22 as default

  echo "DEFAULT_VERSIONS+=apache=2.2" >> /etc/make.conf

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```