It appears that DNS servers will still process a DNS request even if the
z-bit is set, our parser will fail the transaction. So create the
transaction, but still set the event.

Ticket OISF#4924

[Edit by Jason Ish: fix flag bit value]

Ticket OISF#4515

Ticket OISF#4515

Ticket: 4920

Completes commit c8dbe24
which introduced AppProtoEquals to have a generic
check for http in signature can mean http1 or http2 in
traffic.

This commit missed this case, as I only looked for
git grep "alproto ==" and here we deal with
alproto_tc and alproto_ts, but not alproto by itself.

Many places were still referencing the old Suricata page.
Used git grep with replace to update them. Checked that new links work.
Left old references when they were only documentation examples (for
output or unittests).

Task#4915

This commit adds support for enabling libunwind -- a library that can be
used to display stack information.

Libunwind is enabled and used by Suricata if present during
configuration.  A diagnostic message is displayed if libunwind
cannot be found.

This commit adds an error code for the diagnostic code used for
diagnostic messages following unexpected termination due to signals..

This commit adds a configuration setting to enable a stack trace message
if Suricata receives a signal that terminates execution, such as
SIGSEGV, SIGABRT.

This commit adds a signal handler for SIGSEGV when configured. The
signal handler emits a one line stack trace using SCLogError. The intent
is to provide diagnostic information in deployments where core files are
not possible.

The diagnostic message is from the offending thread and includes the
stack trace; each frame includes the symbol + offset.