Plug memory leak, filenames relative to installDir

Plug memory leak, filenames relative to installDir

String options are consistently freed now, before assigning a new value
to them through strdup. The init code now even does use strdup when
setting defaults. This is important for optionslike -lgf, which are not
saved in the settings file, and thus are usually left with their
default. When a dialog to set them then uses free, this causes a crash.
When setting the defaults uses strdup, ParseArgs can already free them.
This plugs an important memory leak, as ParseArgs in now called to parse
the tourney file before every tourney game (twice!), and the lists of
participants and results in it can be quite long.  Macros are defined in
common.h to make the code look simpler.
  Filenames entered through the generic popup are now interpreted
relative to the WinBoard installation folder, just as the saveGameFile
already was. The code handling the atter was made into a subroutine for
this.