Counterintuitive interaction of arguments to ClassWriter(cr, flags)

Currently, no stack map tables are inserted if a method can simply be copied
from ClassReader to ClassWriter. At least to me this is counterintuitive, though.

IMHO, the correct thing to do would be to never copy methods if either
COMPUTE_FRAMES or COMPUTE_MAXS is set. But at the very least the JavaDoc of
ClassWriter(cf, flags) should make this interaction very clear.