configure.ac: use PKG_CHECK_MODULES and AC_PATH_PROG to find protobuf-c

since we're going to depend on protobuf-c 1.x, we now no longer need the
custom MY_CHECK_LIBPROTOBUF_C macro. switch to just using
PKG_CHECK_MODULES to find the library and AC_PATH_PROG to find the
compiler.
google/protobuf-c/protobuf-c.h -> protobuf-c/protobuf-c.h

we now have a dependency on protobuf-c >= 1.x, so we can drop the
"google/" prefixed header paths for the protobuf-c header.
msgmod: replace the the protobuf-c structure size checks with a more robust version number check

we depend on protobuf-c >= 1.x now, so we can use the
PROTOBUF_C_VERSION_NUMBER value exposed by the protobuf-c API to check
compatibility between libnmsg and any transparent message modules (i.e.,
message modules that make use of protobuf-c).

since this changes the nmsg_msgmod_plugin structure, we also need to
bump the msgmod ABI number from 8 to 9.
configure.ac: bump version to 0.9.0
COPYRIGHT: 2014
.travis.yml: libprotobuf-c0-dev -> libprotobuf-c-dev
.travis.yml: install wdns from the wheezy-farsightsec repository instead of building from source
msgmodset: typo mismtach -> mismatch
msgmodset: actually print the major versions on a protobuf-c mismatch
README.md: mention versioned dependency on protobuf-c
README.md: add link to debian farsightsec repository
use my_PKG_CONFIG_FILES
ChangeLog: 0.9.0