fix POST redirects

fix POST redirects

the redirect handling logic compares then method to upper-case strings,
so make sure the method gets upper-cased as well.

add a test to POST to /status/302 on httpbin, which fails against httpbin.org
right now.  i'm submitting a pull request over there to fix that right after
this one.  once that's accepted, the new test verifies that the fix works.