Set _WIN32_IE to 0x500 everywhere and remove where it's not needed.
As we gracefully check if the function is present or not, it's OK to set
this define without having IE 5.0 installed on target
Adds support for a self-contained portable mode in which the
executable's directory is used for application files instead
of directories in the user's profile.
Portable mode is activated by placing a scummvm.ini file in
the executable's directory. The directory must be outside of
the system's Program Files directory to comply with UAC.