setup.py: move import PIL inside generate and add setup_requires on Pillow (#7899)

Also remove double import of re.

setup.py

@@ -7,11 +7,8 @@ import re
 import sys
 import subprocess
 import tempfile
-
 import xml.etree.ElementTree as ET
-import re
-from PIL import Image
-from PIL import PngImagePlugin
+
 
 from distutils.cmd import Command
 from setuptools.command.install_lib import install_lib as _install_lib
@@ -116,6 +113,8 @@ class build_icons(Command):
 
     def generate(self, src, dest, colour, width, **kwargs):
         # default values
+        from PIL import Image
+        from PIL import PngImagePlugin
         author = 'GNOME Project'
         license = 'Creative Commons Attribution-Share Alike 3.0'
 
@@ -173,6 +172,9 @@ setup(
         'XStatic_jQuery',
         'XStatic_jquery_ui',
         ],
+    setup_requires=[
+        'Pillow',
+    ],
     classifiers=[
         'Development Status :: 4 - Beta',
         'Environment :: Web Environment',