Add: Software update directory for aix 6.1 powerpc

Ref: https://dev.cfengine.com/issues/6583

In order for the binary upgrade policy in `update/update_bins.cf` to
work for aix the specific aix version is needed.
Add: Feature to disable checking of cf_promises_validated

Ref: https://dev.cfengine.com/issues/6688

Make it easy to have clients always scan for any changes and update
accordingly.
Merge pull request #340 from nickanderson/option_cf_promises_validated

Add: Feature to disable checking of cf_promises_validated
Merge pull request #327 from nickanderson/redmine/6583

Add: Software update directory for aix 6.1 powerpc
Explain permissive bodies

@nickanderson copying this to 3.6 etc. is up to you...
Merge pull request #342 from tzz/patch-1

Explain permissive bodies
Add: More clear explination of permissive package methods

This is documented in the 3.7 set already, bringing back into 3.6 set
Merge pull request #343 from nickanderson/document_permissive_in_36

Add: More clear explination of permissive package methods
redhat_4 class does not exist on centos_4
When there was an update in master_software_updates, the clients would always refresh the package list. With this change the clients only update the package list weekly. The update will not take longer with this change.