Parse configuration file for ERB (#16878).

Patch by Gavin Dunne.

git-svn-id: http://svn.redmine.org/redmine/trunk@13150 e93f8b46-1217-0410-a6f0-8f06a7374b81
Adds a custom message for when a syntax error occurs (#16878).

git-svn-id: http://svn.redmine.org/redmine/trunk@13151 e93f8b46-1217-0410-a6f0-8f06a7374b81