Added missing newlines at end of files

This fixes g++ compiler warnings.
Remove un-needed const qualifiers on function return types

For g++ (GCC) 4.1.2, this fixes warnings like
cocotb/include/gpi.h:164: warning: type qualifiers ignored on function return type
Merge branch 'gcc_warning_cleanup' of https://github.com/tjora/cocotb into tjora-gcc_warning_cleanup
Merge branch 'tjora-gcc_warning_cleanup'