If itemsize is a power of two use that as the required alignment up tothe maximum provided by the platform. Power of two sizes may be accessedvia larger moves than bytes.Non-power of two sizes are accessed bytewise and can thus always beconsidered aligned.Closesnumpygh-5293

malloc only provides 8byte alignment and is sufficient to load complexon x86 platforms.This fixes the f2py alignment failures with complex types on win32 or onlinux32 with -malign-double