lib.tex: add libimp; remove bogus warning about lineii. libmath.tex: document hypot(). libmd5.tex: rename md5.md5() to md5.new(). libposix.tex: document chown(). libposixfile.tex: openfile() instead of fileopen(). libsocket.tex: document gethostbyaddr(). libtypes.tex: add footnote explaining why readline() keeps the newline. ref3.tex: correct typos, add back*quotes to index. ref4.tex: don't use \verb inside footnote. ref5.tex: explain repr() and str() and add them + back*quotes to index. ref6.tex: correct typo, don't use \verb in footnote. ref7.tex: don't use \verb in footnote.
Added copyright.tex to all files. Added descr of check_interval to libsys.tex. Corrected lotsa typos in tut.tex (thanks to George M. Sipe). Corrected mktuple (should be newtupleobject) example in ext.tex.