Handle specific Debian path: /etc/init.d/ssh instead of /etc/init.d/sshd
cfengine_stdlib.cf: split into 3.4/3.5/3.6 versions.  Add sys.cfengine_version_{major,minor,patch} and use it to load the right libraries for 3.6 and later.  Split by promise type for 3.5 and 3.6.