Merge #539: Assorted minor corrections

52ab96f clean dependendies in field_*_impl.h (Russell O'Connor)
deff5ed Correct math typos in field_*.h (Russell O'Connor)
4efb3f8 Add check that restrict pointers don't alias with all parameters. (Russell O'Connor)

Pull request description:

  * add more checks for restrict pointers.
  * correct math typos.
  * refine dependencies on "num.h"

Tree-SHA512: c368f577927db2ace3e7f46850cb2fdf9d7d169b698a9697767e1f82e9e7091f2b2fea0f7cf173048eb4c1bb56824c884fa849c04c595ee97766c01f346a54ec