Fix various places Valgrind identified as read-of-un-inited. Also
fix use of frequencies are integers: always use a double type explicitly,
which will make MSVC happier.
This is a clean up commit prior to the subsystem API standardisation to simplify
the diffs. It includes all SGSubsystem and SGSubsystemGroup derived classes.
- PTT will now use whatever channel is selected; non zero simply means PTT active.
- The volume as set in the comm[]/radio will now be used as a factor on the FGComm volume
PTT now uses an int channel number (0 means not pressed, 1 = comm radio 1 (index [0]),etc...)
/comm-radio-selected is the default comm channel to use. This should usually be the same as will be set by PTT into /controls/radios/comm-ptt
However PTT will switch the FG comm inbound and outbound frequency to whichever radio was PTT'd.
New properties also set in multi-player to indicate the transmission frequency and normalised power (currently just set to 1.0)
13001(int) : sim/multiplay/comm-transmit-frequency-hz
13002(short-norm) : sim/multiplay/comm-transmit-power-norm
Range for special freq was computed with previous freq, now they are always in range
Use a global variable (_currentFreqKhz) in order to avoid a <static_cast> in main loop; now it's only on frequency change
Fix a .size() > 0 for !.empty()
