Testing that email.message doesn't use the "wrong" casing
email.Generator isn't enough. That would just test that this patch has
been applied. It must also be tested that no other modules uses the
wrong casing of email.Generator. Or other email packages. Or any other
packages at all.

IMHO the "right" test would be to test that modulefinder can find all
relevant modules in all cases. The problem is that it gives irrelevant
warnings.

I tested with some shell hacking to find all modulefinder failures which
could be found with another casing:

find * -name '*.py'|sed 's,\.py$,,g;s,/,.,g;s,\.__init__$,,g' >
/tmp/all_fs_modules
for a in $(find * -name '*.py'); do echo $a; python -m modulefinder $a;
echo; done > /tmp/all_referenced_modules
for a in $(grep ^? /tmp/all_referenced_modules|sed 's,^\? \(.*\)
imported from .*,\1,g'|sort|uniq); do grep -i "^$a"'$'
/tmp/all_fs_modules; done > /tmp/referenced_existing_ignorecased

email.base64mime
email.charset
email.encoders
email.errors
email.generator
email.header
email.iterators
email.message
email.parser
email.quoprimime
email.utils
ftplib

- where the last hit comes from bogus regexp matching. The test takes
long time to run as it is. That could probably be improved. But still I
think this is to be compared with "lint"-like tools which should be run
reguarly but isn't suitable for unit tests.

I feel ashamed for arguing against introducing a test. I think I do that
because I think that this isn't a "normal" bug and thus isn't suitable
for unit testing. 

The email module itself really is fully backwards compatible. And
modulefinder does a good job doing what it does and can't be blamed for
not figuring the email hackery out. The problem comes when a third
external modules puts things together and they doesn't fit together as
one could expect.

Also, currently both casings works and should work. Using the old casing
isn't a "bug bug", but it has consequences which IMHO is enough to call
it a bug and fix it.

Perhaps Python could have a standard way markup of deprecated functions
so that it could be checked that the standard librarary didn't use them.