BndEditModel: keep the changes to save sorted.

So that the resulting (generated) bnd.bnd file will look a bit nicer.

Signed-off-by: Ferry Huberts <ferry.huberts@pelagic.nl>
The verifier was too whiny about unresolved references. So reverted
to only check this if the bundle was not build by bnd. Too many
people were actually excluding imports.
Uses constraints caused problems because some packages
are not exported from the junit bundle. So removed the uses.
Reinstated automatic continuous, too big a change
Set verbose=false
The -runfw was treated as a Just In Time variable, i.e. it was initialized when it was needed and not eagerly. However, the JIT used the fact that the variable was empty to do the initialization. This works fine, unless you do not clear this variable in the prepare(). This caused -runfw to to be 'unalterable' once it had a member. 

Added this variable to the clear list ...