Validation Fixes

[dcousens]

This pull request makes some mild progress towards improving the quality of the point validation functions.
Most of the important issues have been discussed on IRC, but some key points where things will need to change in the future (but are not implemented in this pull request) are:

• Change params.curve.params to be curve.params, that is, return a curve object from names.js, not a parameters object.
• Move all the group operations to this new Curve object and remove the Point object completely.
  It is just bloat, and there should never be a case where two points are not in the same curve context and group operations performed. So it is useless storage and a possibility for error.

[coveralls]

Coverage increased (+1.82%) when pulling 29dde30 on dcousens:validatepass into 2721aba on cryptocoinjs:master.

[jprichardson]

@dcousens Practically, this seems pretty good. Good enough? Is this an edge case that you think will really matter or probabilistically speaking, ever be a concern?