Fix mod::prefork dependencies

A dependency on the package resolves the following error:
"Error: /Stage[main]/Apache::Mod::Prefork/File_line[/etc/sysconfig/httpd
prefork enable]: Could not evaluate: No such file or directory -
/etc/sysconfig/httpd"
Use correct template for dav_fs module
Merge pull request #188 from nanliu/prefork

Fix mod::prefork dependencies
Merge pull request #194 from mxey/master

Use correct template for dav_fs module