in HSEFunctional define static function that evaluates FT of the erfc(wr)/r potential
screening omega must be static, so that this function can use it

bugfixes in local xc energy
use a instead of (1-a) [a = 1/4]
add ec += h line in nonmagnetic correlation energy

git-svn-id: http://qboxcode.org/svn/qb/branches/hse-dev@1385 cba15fb0-1239-40c8-b417-11db7ca47a34