Internal transform API was very confusing. For example, rotate method was calling self.transform or self.im.rotate depends on expand argument, but self.im.rotate internally also calls ImagingTransformAffine, so it was excessive.

Changes proposed in this pull request:

• First of all, this PR fixes rotations bug Image.rotate(90*n, expand=True) results in translation and expansion #1917 in two ways:
  • It really uses very cheap transpose operations if it is possible regardless of filter. 8203a43
  • It rounds coefficients in the transform matrix, so even if we are not using cheap transpose, we still get right dimensions because cos(90°) now is exactly 0, not 6.123e-17. 7687ce8
• Image.rotate always uses self.transform, so im.rotate was removed from core library. 709078e 1f8c252
• The order of coefficients in internal API now match matrix representation and order of external API. 2b77b1c 3d622d6
• Internal ImagingTransformAffine, ImagingTransformPerspective and ImagingTransformQuad was replaced with one entry point to all transformations: ImagingTransform. Former ImagingTransform was renamed to ImagingGenericTransform and removed from extern symbols (Imaging.h file). 6be3df2 9902d2e