Cleanups and comments for pyramid sequence header.
Cleanups and comments for pyramid sequence header.

Nazg-Gul/libmv,rgkoo/libmv-blender,libmv/libmv,SoylentGraham/libmv,SoylentGraham/libmv,SoylentGraham/libmv,keir/libmv,libmv/libmv,petertsoi/libmv,petertsoi/libmv,libmv/libmv,petertsoi/libmv,keir/libmv,rgkoo/libmv-blender,Nazg-Gul/libmv,rgkoo/libmv-blender,rgkoo/libmv-blender,rgkoo/libmv-blender,Nazg-Gul/libmv,keir/libmv,SoylentGraham/libmv,petertsoi/libmv,keir/libmv,Nazg-Gul/libmv,libmv/libmv,Nazg-Gul/libmv