added aix support

- added aix sudo parameters to params.pp

- introduced a new parameter package_source which is required for the
  aix sudo installation (rpm based)

- introduced a new class package for the package installation

- init.pp now uses class package for the actual installation

- in package.pp we use a dedicated class for the aix package installation
  as the aix package has additional dependencies and we have to resolve
  them manually (don't ask...)

  the standard package installation is the same as in the previous
  version of init.pp
Merge pull request #32 from tosmi/aix

added aix support