Install dummy handler for SIGHUP.
Set match->location.
Add a '-t' option to check the configuration file.
"groups" is a global variable.

  Hopefully this doesn't break anything
Reload configuration on SIGHUP.
The '-t' option now takes a filename as argument.
Somewhat safer reload of the externals file.
Use signal-safe-type for flag.

While here use slightly a shorter variable name, and marginally more accurate
logging message.
Tabs to spaces.
Remove dead code.