POSIXUsers: set managed uid/gid range

Added options to set a range (whitelist or blacklist) of managed
uids/gids so that accounts in LDAP (e.g.) do not get flagged as
"extra" entries.

Request: http://article.gmane.org/gmane.comp.sysutils.bcfg2.devel/4629
GroupPatterns: improved PackedDigitRange and tests
docs: added docs for POSIXUsers uid/gid ranges
Properties: fixed lax/strict decryption setting with no crypto libs installed
Merge branch 'master' into 1.3.1

Conflicts:
	src/lib/Bcfg2/Server/Plugins/Properties.py
StructFile: fixed lax/strict decryption setting with no crypto libs installed