Closes #290

Closes #276

copy_body() used to treat chunked encoding (or at least reading from
wsgi.input without a valid Content-Length, could be user provided
body_file_raw and didn't set Content-Length) with no consideration for
the amount of data that could be on the other end.

This could potentially allow for a VERY large python bytes() object to
be allocated followed by a very large BytesIO(), which then one line
later it would copy to a temporary file, damage already done.

The new changes will read up to Content-Length if it is available, if
not but the body is still marked readable, it will attempt to read from
the input until it is exhausted.

Up to req.request_body_tempfile_limit will be stored in a BytesIO, after
that it will instead write it to a temporary file. So even if the other
end is sending 100's of MB worth of data it won't blow up your Python
process.

You can now set req.body for any request method.

This also changes req.from_file in that now it will attempt to read the
entire file for the body if no Content-Length is set, even if the
request method generally does not have a body (such as GET/DELETE).

This has been deprecated since WebOb 1.2 and non-functional for a long
time.