small patch to make dreaded LoadErrors easier to track down

Could we get this small patch applied?

It adds a log warning to help track down the cause of the dreaded:
"LoadError: Expected /foo.rb to define Foo" message. These errors can
be frustrating to track down, as they are almost always related to
missing dependencies or slight typos in constant names, and are
probably total show stoppers for newbies.

- Rob

Added verified tag based on prior +1's, it is in report 12 now...

A general note on ticket verification:

Please do not +1 if you did not actually verify the patch. That means
applying it, testing Rails, and testing your app. Otherwise, three +1
would culminate in 'popular', not 'verified', and report 12 would no
longer be a useful list of ready-to-commit patches.