Improve error handling to always throw exceptions and never abend

We're interested in funding a fix to ensure errors are always thrown as exceptions, as mentioned here: https://issues.civicrm.org/jira/browse/CRM-11193 and here: #395 and here: #749 (closed)

If someone could tag this with 'paid-issue-queue' I'd appreciate it.

Our particular interests are:

• catching errors when generating groups for mailings. Currently if these fail a mailing can cheerily sail on without the correct exclusion group
• catching smarty errors in mailings. These currently fail silently and can kill the scheduled jobs list

It seems like both of these are covered by CRM-11193.

I'm not promising we can fund the whole thing, but we can at least pay for time spent investigating what needs to be done.