fs_encode: load mod_spandsp before loading mod_native_file so that the latter picks up all the codecs offered by the former

Apparently the Raspberry Pi blows up (out of memory) if you call
dpkg-source -z9 as it implicitly calls xz -9.  Thanks to Ken Rice for
running headlong into this.

Also note that while xz takes -0, dpkg-source won't take -z0, so we
check for this and make sure we call dpkg-source correctly.

Ken thinks this may have been needed to get mod_portaudio to work for
him.

Freetdm - ISDN:Fix for race condition where we receive a new call, and did not finish clearing existing call internally.