Added first cut of the non-central chi squared distribution.
Removed almost all occurrences of real_cast: replaced with calls to the truncation/rounding functions instead.
[SVN r42744]
Added new optimisation config options (still need documenting).
Tidied up use of instrumentation code so they all use BOOST_MATH_INSTRUMENT now.
Various tweaks to inverse incomplete beta and gamma to reduce number of iterations.
Changed incomplete gamma and beta to calculate derivative at the same time as the function (performance optimisation for inverses).
Fixed MinGW failures.
Refactored and extended rational / polynomial test cases.
[SVN r4172]
