DSLError prints the specific line in a Gemfile where the error was
raised. That's helpful when the error was explicitly raised by the
Gemfile DSL or, in the case it's implicitly raised, when the offending
code lives right in the Gemfile.

If it's an internal error, or something buried dowm in user code called
from the Gemfile, `DSLError` is not helpful since it hides the actual
culprit.

This commit tries to only raise `DSLError` in the cases mentioned above
and otherwise let the original error be raised.

https://github.com/rubygems/rubygems/commit/b30ff5a682

https://github.com/rubygems/rubygems/commit/bb66253f2c

This is in preparation for deprecating source-less gemfiles.

https://github.com/rubygems/rubygems/commit/d6493fa3e2

https://github.com/rubygems/rubygems/commit/4d1a0c465a

https://github.com/rubygems/rubygems/commit/ade0c441d5

https://github.com/bundler/bundler/commit/5946d62ad0