Description of problem:

$ sudo yum install @NOSUCHGROUP
Loaded plugins: auto-update-debuginfo, langpacks
Nothing to do
$ echo $?
0

But if you try that with an ordinary package:

$ sudo yum install NOSUCHPACKAGE
Loaded plugins: auto-update-debuginfo, langpacks
No package NOSUCHPACKAGE available.
Error: Nothing to do
$ echo $?
1

Version-Release number of selected component (if applicable):

yum-3.4.3-106.fc19.noarch

How reproducible:

100%

Steps to Reproduce:
1. See above.

Expected results:

Yum should give an error (and MORE IMPORTANTLY return a
non-zero exit code) if the group does not exist.