luasocket/FIX

url.absolute was not working when base_url was already parsed
http.request was redirecting even when the location header is empty
tcp{client}:shutdown() was checking for group instead of class.
tcp{client}:send() now returns i+sent-1...
get rid of a = socket.try() in the manual, except for protected cases.
    replace it with assert.
get rid of "base." kludge
check all "require("http")" etc in the manual.
make sure sock_gethostname.*  only return success if the hp is not null!
change 'l' prefix in C libraries to 'c'
    don't forget the declarations in luasocket.h and mime.h!!!
setpeername was using udp{unconnected}
fixed a bug in http.lua that caused some requests to fail