net.c v 1.05 (add 522 timeout)

Add timer to detect timeout.
Use Alarm clock signal.
The server now will respond a 522 timeout error after 15 seconds.
Also change the type of buffer from char to unsigned char to solve a
warning text.
Merge pull request #14 from lzhang25/master

net.c v 1.05 (add 522 timeout)