Improve deployment exception message if selected/enabled alternative/interceptor/decorator class is not part of the synthetic bean archive

Right now, a too general message like "Enabled alternative X is not an alternative" is used. Something like "Enabled alternative X is not a bean class of the synthetic bean archive" will be more useful. We will have to detect this error during org.jboss.weld.environment.se.Weld.initialize().
This is also not consistent comparing to enabled interceptor/decorator which are automatically added to bean classes so we will remove this automatic addition.