Add index-based constructors to rate helpers.
Export swap-helper constructors with discounting curve.
Export overnight indexes.
Export OIS rate helpers.
Updated SWIG bindings for rate helpers.

Where allowed by the underlying library, helpers can now
use and external discount curve. Missing overloads of the
constructors were also exported.
Fixed arguments passed to CmsLeg in test case.

I'm not sure how this was working previously. It's likely that
SWIG 2.0.x used less strict type checks and allowed conversion
to and from booleans. SWIG 3.0 no longer allows this.
Ignored artifact from newer Perl tools.
Added China Inter Bank Holiday calendar

China Inter Bank holidy schedule is different from SSE (Shanghai
Securities Exchange). Some weekends are good working days for inter bank
market. Now the working weekends are hard coded for the years 2013 and
2014
Replace hard tabs with spaces.
Include required header only.
Rename inner class for consistency.
Hide implementation of working weekends as set.
Export new interbank Chinese calendar.
Merge pull request #93.