configure.ac: check for required header file nmsg/sie/dnsdedupe.pb-c.h
dnstable_dump: newline delimiter fix when printing entries

we need to add a newline between entries in print_entry() for all modes
except when printing rdata entries in the text format. prior to this
change we were not emitting newlines when printing rdata entries in JSON
format.
configure.ac: check for required header file google/protobuf-c/protobuf-c.h
.travis.yml: new