B"H web ui: backend - check ground validity before altitude validity

Before, even when an aircraft was on the ground, validaltitude was 1
instead of -1. This is because when MODES_ACFLAGS_ALTITUDE_VALID flag
was true, no further checking would be done, and validaltitude would be
set to 1. However, the MODES_ACFLAGS_ALTITUDE_VALID can be true when the
aircraft is on ground, so the ground status must be checked before the
altitude validity flag.
B"H decoding: use last air position to calculate ground position
Merge pull request #23 from hhm0/decoding

use last recent airplane position to calculate its ground position
Merge branch 'master' of https://www.github.com/MalcolmRobb/dump1090 into web_update
Version 1.09.1007.14

Updates to support COAA Planeplotter Ground Station on an RPi
Version 1.09.1607.14

Improvements to COAA MLAT functions
Reduce CPU load in PPUP1090 and DUMP1090 during cleanup
Tidy up interactive.c

Remove spaces from the end of line.
net_io port 30003 bug

Thanks to "Harrie" for this one.
Fix the SBS port 30003 stream to always include speed and/or heading
when available.
Version 1.09.0608.14

Release of COAA PlanePlotter MLAT and SMU support for RPi

ppup1090 now supports Ground Stations functions required for MLAT and
SMU operation. This is *ONLY* available for RPi and similar linux
hardware.

Also included are sample startup scripts for dump1090 only and
dump1090+ppup1090 together.
Merge branch 'master' of https://www.github.com/MalcolmRobb/dump1090 into web_update