Add parameter for purging vdir

The new parameter $purge_vdir in apache class gives the possibility to disable the purging of the virtual hosts directory.
Restrict the versions and add 3.1

~> 2.6 will match 2.7
Merge pull request #159 from richardc/patch-1

Restrict the versions and add 3.1
Merge pull request #139 from mjanser/patch-1

Add parameter for purging vdir