BLD: fix issue with bdist_egg, which made make dist in doc/ fail

This issue came in because of commit 9b3f650 a month ago.
`bdist_egg` has always been missing from the command list, but
that wasn't a problem because missing commands were simply
ignored by the validation. After that commit we started raising
a RuntimeError instead.

setup.py

@@ -257,7 +257,8 @@ def parse_setuppy_commands():
     # below and not standalone.  Hence they're not added to good_commands.
     good_commands = ('develop', 'sdist', 'build', 'build_ext', 'build_py',
                      'build_clib', 'build_scripts', 'bdist_wheel', 'bdist_rpm',
-                     'bdist_wininst', 'bdist_msi', 'bdist_mpkg', 'build_src',)
+                     'bdist_wininst', 'bdist_msi', 'bdist_mpkg', 'build_src',
+                     'bdist_egg')
 
     for command in good_commands:
         if command in args: