tests: Add check for handling of wide data (16 probes)

The details of the test are explained in-source. This test is designed to
provide a test case for bug 33.

Signed-off-by: Alexandru Gagniuc <mr.nuke.me@gmail.com>
global: Do not assert >= 0 for unsigned values

Unsigned values are always >= 0. These assertions are redundant, so remove them.

$ grep assert -r ./ |grep ">=" |grep 0
shows the assert(something >= 0). Remove those which assert(unsigned >= 0).

Signed-off-by: Alexandru Gagniuc <mr.nuke.me@gmail.com>
Fixed usage of sr_datafeed_logic::length

The length field is a measure of bytes not samples. The previous
usage would fail unless the unitsize was set to 1.
Fixed LongPulses test packet setup

The length field is now populated with the number of bytes rather
than the number of samples
Added Sixteen test case

This test case is a replica of sixteen.sr attached to the Bug #33
Do not fast_forward if there is no data at the minimum mip-map level
Added File>Quite menu item