Description of problem:
While it is said in manual that .service is the default unit type assumed when no suffix is specified it does not always work. For example 'is-enabled' command fails while 'start', 'stop', 'status' and 'show' work.

Version-Release number of selected component (if applicable):
systemd-44-23.fc17.x86_64

How reproducible:
Always

Steps to Reproduce:
1."systemctl is-enabled abrtd"
  
Actual results:
Failed to issue method call: Invalid argument

Expected results:
enabled