Use sqlite_ext 1.5.0 which has been broadened to work with Ruby
versions prior to 2.x, and remember to add it to files in the
./gemfiles/ directory for use with CI tests, not just to
Gemfile in the root directory.

Switch to byebug for MRI 2.x debugging.  Debugger is not supported for 2.1.2 and up, and was never fully 2.x compatible.

Fixes the problem described here:
https://github.com/mongoid/mongoid/issues/2579

This should be reverted when the Mongoid issue (or whatever it is)
is fixed.

Geocoder should be required after other things like Rails and Mongoid.

Also update contents of .gitignore from same.