Update protobuf-c to 1.3.0

protobuf-c (1.3.0)

  [ Robert Edmonds ]
  * Release 1.3.0.
  * Add test case for the issue in #220 (#254).
  * Fix issue #251, "Bad enums with multiple oneofs" (#256).
  * Add warning flags to my_CFLAGS (#257).
  * Fix namespace errors when compiled with latest protobuf (#280).
  * Bump minimum required header version for proto3 syntax (#282).

  [ Paolo Borelli ]
  * Turn the compiler into a protoc plugin (#206). This allows the protobuf-c
    compiler to be invoked as "protoc --c_out=...". For backwards
    compatibility, we still ship a protoc-c command, but it's a symlink to the
    protoc-gen-c binary.
  * proto3 support (#228).
  * Remove leftover FIXME comment (#258).
  * Fix proto3 "is zeroish" evaluation (#264).
  * Small cleanup in oneof handling (#265).
  * Rework is_zeroish one more time (#267).
  * proto3: make strings default to "" instead of NULL (#274).

  [ Tomek Wasilczyk ]
  * Fix -Wsign-compare warnings (#213).
  * Fix ISO C90 -Wdeclaration-after-statement warnings (#214).
  * Fix bigendian -Wunused-label warning (#215).

  [ Ilya Lipnitsky ]
  * protoc-c/c_message.cc: Force int size on oneof enums (#221). Fixes wrong
    enum generation and handling for onceof cases (#220).

  [ Adnan ]
  * Fix cmake build if built as part of an external project (#231).

  [ Gregory Detal ]
  * Remove .pb.{cc,h} in distdir instead of top_distdir in order to prevent
    removing files from other projects when protobuf-c is included as an
    autotools subproject (#232).

  [ Ben Farnham ]
  * Relax autoconf constraint from v2.64 to v2.63 so that it works on older
    Linux distros (#233).

  [ Thomas K旦ckerbauer ]
  * rm argument fix for Solaris (#234).
  * Add 'const' qualifier to 'init_value' variable in generated files (#236).

  [ Richard Kettlewell ]
  * Document and extend the effect of passing NULL to ..._free_unpacked
    functions (#255).

  [ Alex Milich ]
  * CMake: Workaround for static builds that use MSVC (#243).

  [ Josh Junon ]
  * CMake: Allow protobuf-c to be included via include_subdirectory (#245).

  [ Alexei Kasatkin ]
  * CMake: Windows fixes (#266).

(wiedi)