wxWidgets 3.1 has deprecated wxPATH_NORM_ALL when normalizing file
paths when calling wxFileName::Normalize(). This change keeps the
existing behavior except in places where our own internal
ExpandEnvVarSubstitutions() to expand environment variables.
The same logic block to resolve possible symlinks exists in 5 different
places now. This change moves this duplicated code to a static member
function of WX_FILENAME instead.
Wayne Stambaugh
Johannes Maibaum
Marek Roszko