[tests] Disable long double tests when not supported.
[non-central-t] Reorganize tests a little.
[polygamma] Fix expected error rates when BOOST_MATH_NO_LONG_DOUBLE_MATH_FUNCTIONS is defined.
[examples] Disable initializer list tests for gcc-4.4.x as the compiler doesn't seem to support then even though it has <initializer_list>.
[hyperexponential] Disable initializer list tests for gcc-4.4.x as they seem not to be supported.
[tgamma] Up expected error rates - some are too tight for intel-linux.
[polygamma] Fix preprocessor code SNAFU.