problem was a couple of bugs in the readline implementation.
1. Include the '\n' in the string returned by readline
2. Bug calculating new buffer size in _unread
Also remove unncessary import of StringIO
Here's my suggested replacement for gzip.py for 1.5.1. I've
re-implemeted methods readline and readlines, added an _unread, and
tweaked read and _read.
I tried a more complicated buffer scheme for unread (using a list of
strings and string.join), but it was more complicated and slower.
This version is a lot faster than the current version and is still
pretty simple.
