fixed missing integer conversions in wigner.py

The definitions of imax, imin, and maxfact (in gaunt, wigner_9j, racah, and _big_delta_coeff) are always guaranteed to of integer value by triangle conditions that are tested before these variables defined.  However, when computing coefficients for half-integer spins, these variable are left as a floats (ex imax = 10.0 not imax = 10).  These definitions have now been guarded with int()