Delete self->protobuf before freeing the object in osm.cc

tp_free() also free the protobuf entry of the object. This means that the
following delete could use an incorrect address, and lead to a segfault.
Merge pull request #13 from jocelynj/fix-segfault

Fix a segfault in OSMBPF.so
Merge branch 'master' of github.com:omniscale/imposm-parser
update CHANGES for 1.0.6
bump version for next release