fixes #168: sox options deprecated in 13.0.0 (Feb 2007) and removed in 14.1.0 (July 2008) should no longer be used

This fixes an issue where sox mysteriously identifies itself with an empty version string (which could be cast to 0), observed on OSX 10.8 with SoX installed through MacPorts:

```
$ port installed sox
  sox @14.4.1_2 (active)
$ sox --version
sox:      SoX v
```

Finally, the external program checker no longer caters to older sox versions (if you're stuck with an ancient sox, you have much bigger problems to worry about!)
fixes #169: Tcl scripts should explicitly exit to avoid hanging issues with popup GUIs

Also, make `getf0.tcl` scripts non-executable, since the shebang will only be valid on a minority of systems
rerun autoconf to update configure scripts
fixes #170
change extension of feature example files for good measure

see also https://github.com/marytts/marytts/issues/70#issuecomment-7897356