Description of problem:

When adding project maintainers,
pressing "Enter" on username search field should:
Search the usernames that start whith the search term.
and show either 
1) a user seletion box if there is multiple matches, or
2) the actual name and email address if there is only one match.

However, current behavior of "Enter" is dialog will be closed if there is only one match.

Version-Release number of selected component (if applicable):
Zanata version 1.8.0-SNAPSHOT (20120904-0014)

How reproducible:
Always

Steps to Reproduce:
0. Sign in as a project maintainer.
1. Visit any project you maintain, and click "Manage Maintainers"
2. Click Action "Add Project Maintainer"
3. Type any valid username and press "Enter"


Actual results:
"Add Project Maintainer" dialog get closed and nothing else happend.

Expected results:
"Add Project Maintainer" dialog remain opened, 
search the usernames that contain the string as prefix.
and show either 
1) a user seletion box if there is multiple matches, or
2) the actual name and email address if there is only one match.