class FieldStorage: this patch changes read_lines() and co. to use a
StringIO() instead of a real file. The write() calls are redirected
to a private method that replaces it with a real, external file only
when it gets too big (> 1000 bytes).
This avoids problems in forms using the multipart/form-data encoding
with many fields. The original code created a temporary file for
*every* field (not just for file upload fields), thereby sometimes
exceeding the open file limit of some systems.
Note that the simpler solution "use a real file only for file uploads"
can't be used because the form field parser has no way to tell which
fields correspond to file uploads.
It's *possible* but extremely unlikely that this would break someone's
code; they would have to be stepping way outside the documented
interface for FieldStorage and use f.file.fileno(), or depend on
overriding make_file() to return a file-like object with additional
known properties.
added test script and expected output file as well
this closes patch 103297.
__all__ attributes will be added to other modules without first submitting
a patch, just adding the necessary line to the test script to verify
more-or-less correct implementation.
