BUG/MINOR: tcp-check: don't condition data polling on check type

tcp_check_main() would condition the polling for writes on check->type,
but this is absurd given that check->type == PR_O2_TCPCHK_CHK since this
is the only way we can get there! This patch removes this confusing test.
(cherry picked from commit e7b9ed33ee7306c1f9fd276bb5e683befab06e82)
BUG/MEDIUM: tcp-check: don't rely on random memory contents

If "option tcp-check" is used and no "tcp-check" rule is specified, we
only look at rule->action which dereferences the proxy's memory and which
can randomly match TCPCHK_ACT_CONNECT or whatever else, causing a check
to fail. This bug is the result of an incorrect fix attempted in commit
f621bea ("BUG/MINOR: tcpcheck connect wrong behavior").

This fix must be backported into 1.5.
(cherry picked from commit d2a49592faca66381303d8e0d63665ae44046def)
BUG/MEDIUM: tcp-checks: disable quick-ack unless next rule is an expect

Using "option tcp-checks" without any rule is different from not using
it at all in that checks are sent with the TCP quick ack mode enabled,
causing servers to log incoming port probes.

This commit fixes this behaviour by disabling quick-ack on tcp-checks
unless the next rule exists and is an expect. All combinations were
tested and now the behaviour is as expected : basic port probes are
now doing a SYN-SYN/ACK-RST sequence.

This fix must be backported to 1.5.
(cherry picked from commit f3d3482c984593b21a6d3de6d66a83a338316b85)