DWORD WINAPI ExpandEnvironmentStr( const char *Src, char *Dest, size_t Size );
%VariableName%.
For each such reference, the %VariableName% portion is replaced
with the current value of that environment variable.
The replacement rules are the same as those used by the command interpreter.
Case is ignored when looking up the environment-variable name. If the name is not
found, the %VariableName% portion is left unchanged.