well_controls_equal(): Don't compare set capacities

The 'cpty' field is for internal memory management purposes only.
No client can know of its existence, let alone inspect or directly
change the value, so it should not be used to adjudicate control set
equality.  This was useful during the refactoring work to introduce
the opm-parser support, but its utility has since ceased.

Okay'ed by: [at] atgeirr and [at] joakim-hove
clone_wells(): Assert result equal to input

This adds a debug-mode safety belt that cloning wells produces a
comparable set of wells to the input.
well_controls: Add deep-copy (clone) support

New function well_controls_clone(), implemented in terms of the
public API only, mirrors the objective of function clone_wells(),
only for well control sets.  Add a basic test to demonstrate the
function too.
wells.h: Document several function

This commit adds Doxygen-style documentation to functions

  - clear_well_controls()
  - set_current_control()
  - wells_equal()

No functional changes.
Reimplement clone_wells() in terms of well_controls_clone()
Merge pull request #612 from bska/resv-support

Implement deep copy operation for struct WellControls