Signed-off-by: Piotr Sikora <piotr@cloudflare.com>

If seek position is within the last track chunk
and that chunk is standalone (stsc entry describes only
this chunk) such seek generates stsc seek error. The
problem is that chunk numbers start with 1, not with 0.

Mp4 module does not check movie and track durations when reading
file.  Instead it generates errors when track metadata is shorter
than seek position.  Now such tracks are skipped and movie duration
check is performed at file read stage.

Mp4 module does not allow seeks after the last key frame.  Since
stss atom only contains key frames it's usually shorter than
other track atoms.  That leads to stss seek error when seek
position is close to the end of file.  The fix outputs empty
stss frame instead of generating error.

If there is no SSI context in a given request at a given time,
the $date_local and $date_gmt variables used "%s" format, instead
of "%A, %d-%b-%Y %H:%M:%S %Z" documented as the default and used
if there is SSI module context and timefmt wasn't modified using
the "config" SSI command.

While use of these variables outside of the SSI evaluation isn't strictly
valid, previous behaviour is certainly inconsistent, hence the fix.

This adds support so it's possible to explicitly disable SSL Session
Tickets. In order to have good Forward Secrecy support either the
session ticket key has to be reloaded by using nginx' binary upgrade
process or using an external key file and reloading the configuration.
This directive adds another possibility to have good support by
disabling session tickets altogether.

If session tickets are enabled and the process lives for a long a time,
an attacker can grab the session ticket from the process and use that to
decrypt any traffic that occured during the entire lifetime of the
process.

This fixes content type set in stub_status and autoindex responses
to be usable in content type checks made by filter modules, such
as charset and sub filters.