detect inconsistency / corruption / hash collision, closes #170
detect inconsistency / corruption / hash collision, closes #170

added a check that compares the size of the new chunk with the stored size of the
already existing chunk in storage that has the same id_hash value.
raise an exception if there is a size mismatch.

this could happen if:

- the stored size is somehow incorrect (corruption or software bug)
- we found a hash collision for the id_hash (for sha256, this is very unlikely)

edgewood/borg,edgimar/borg,edgimar/borg,level323/borg,RonnyPfannschmidt/borg,RonnyPfannschmidt/borg,level323/borg,mhubig/borg,raxenak/borg,mhubig/borg,edgimar/borg,RonnyPfannschmidt/borg,raxenak/borg,RonnyPfannschmidt/borg,edgewood/borg,edgimar/borg,edgewood/borg,mhubig/borg,raxenak/borg,raxenak/borg,RonnyPfannschmidt/borg,edgewood/borg,level323/borg