Update to RSpec 2.12.  #3496.

I want to be able to use parameterized shared contexts in my response
set populator tests.  (In my case, the parameter is the name of a test
survey that will be loaded in a before-all.)  This capability doesn't
exist in RSpec 2.6.

Said capability was probably introduced sometime before 2.12, but I've
been using 2.12 for a while and it seems stable enough, so might as well
just use it.
New response set prepopulation pattern.  #3496.

There are no specs in this commit, and therefore I have no idea if this
works.  Topic branches, etc.

The new prepopulators will be filled in from existing code in future
commits.
Adapted birth response set prepoulator to new api. #2744
Adapted child and adhoc response set prepoulator to new api. #2744
Responses set prepoulation child classes should inherit from parent. #2744
Adapted non interview response set prepoulator to new api. #2744
Adapted participant verification response set prepoulator to new api. #2744
Adapted postnatal response set prepoulator to new api. #2744
Adapted pregnancy visit response set prepoulator to new api. #2744
Adapted tracing response set prepoulator to new api. #2744
Adapted pbs eligibility screener response set prepoulator to new api. #2744
Adapted low intensity response set prepoulator to new api. #2744
Implement skeleton helper methods in base response set prepoulator. #2744
Removing method which exists in parent class. #2744
Ordered methods to be identical to original response set populator. #2744
Fix incorrectly named class name. #2744
Adding missing method from old response set prepopulator. #2744
Segregate old data access code.  #3496.