This is r61508 plus additional fixes to the handling of 'limit'

This is r61508 plus additional fixes to the handling of 'limit'
in TextIOWrapper.readline().

All tests now pass for me (except for expected skips on darwin:
bsddb, bsddb3, cProfile, codecmaps_*, curses, gdbm, largefile,
locale, normalization, ossaudiodev, pep277, socketserver,
startfile, timeout, urllib2net, urllibnet, winreg, winsound,
xmlrpc_net, zipfile64, and the -u largefile part of test_io).