Fixes compatibility with third-party modules.

This patch also adds argument checking to all socket methods.

(fix httpd log messages)

(so user can use 'SO_REUSEADDR' option in tcp_server)

This patch fixes out of bounds memory access in bit_iterator_init
for size == 0. The patch also optimizes bitset/index library to skip
useless iterations over empty keys.

Closes #425

No test case since we don't test contents of the log in 1.5.

Add a testcancel() call to iowait().
A test case will be added to 1.6, where it's easier to do.

This patch fixes tcp_connect() for case when server sends
some data immediately after connect.

This patch fixes logic of non-blocking tcp connect as it
described in man pages and Unix Network Programming vol.1.

The bug was in the test itself - lack of trailing 0
at the end..

Fix a build warning on FreeBSD i386

Update the user guide.