Add endian check and define ISIS Endian Macro
Add endian check and define ISIS Endian Macro

This is a pretty big item that I missed. It means we've been
interpreting special pixels incorrectly in ASP. This was also breaking
mroctx2isis.

NeoGeographyToolkit/AutotoolsForISIS,NeoGeographyToolkit/AutotoolsForISIS,NeoGeographyToolkit/AutotoolsForISIS