Change: Fix default mailfrom

Ref: https://dev.cfengine.com/issues/6567

$(sys.host) is ambiguous and the old usage may produce a mailfrom of
root@foo.example.org.example.org for host "foo" in domain "example.org".
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.
Merge pull request #341 from nickanderson/pick_redmine/6583

Add: Software update directory for aix 6.1 powerpc
Merge pull request #334 from nickanderson/pick_redmine/6567

Change: Fix default mailfrom
Change: Clarify documentation on permissive package_methods

Picking from master into 3.6.x branch
Merge pull request #344 from nickanderson/pick_permissive_doc_fix

Change: Clarify documentation on permissive package_methods
redhat_4 class does not exist on centos_4

(cherry picked from commit c0e65d29e55330c31c12bd1632ccd09d9a267c4d)

Conflicts:
	lib/3.7/packages.cf
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.

(cherry picked from commit 699cc3ef05d12a5b15171a303541bb2ea515fb0d)