Blender Git Loki

Cleanup: link/append: get rid of booleans in func parameters.

One or two are OK, but more make it rather unreadable, and future work
is likely to require more toggle specific behavior here. So switched to
bitflags, switching from short to int and using 16 upper bits for
'internal' ones defined in BLO_readfile.h, combined with 'public' ones
from user interaction, defined in DNA_space_types.h