Bump minimum protobuf version to 2.5.0

t/test-full.proto: Add option_allow alias to the duplicate value test
enum
travis-ci: Download protobuf 2.5.0 and build from source, since Travis
uses an older Ubuntu 12.04 with protobuf-c 2.4.0

.travis.yml

@@ -9,7 +9,14 @@ before_install:
     - sudo apt-get update -qq
 
 install:
-    - sudo apt-get -q install protobuf-compiler libprotobuf-dev libprotoc-dev valgrind lcov
+    - wget http://protobuf.googlecode.com/files/protobuf-2.5.0.tar.gz
+    - tar -xzvf protobuf-2.5.0.tar.gz
+    - cd protobuf-2.5.0 && ./configure
+    - make -j8
+    - sudo make install && sudo ldconfig
+    - cd ../
+
+    - sudo apt-get -q install valgrind lcov
     - sudo pip install cpp-coveralls
 
 script:

configure.ac

@@ -47,7 +47,7 @@ AC_ARG_ENABLE([protoc],
   AS_HELP_STRING([--disable-protoc], [Disable building protoc_c (also disables tests)]))
 if test "x$enable_protoc" != "xno"; then
   AC_LANG_PUSH([C++])
-  PKG_CHECK_MODULES([protobuf], [protobuf])
+  PKG_CHECK_MODULES([protobuf], [protobuf >= 2.5.0])
 
   save_CPPFLAGS="$CPPFLAGS"
   CPPFLAGS="$save_CPPFLAGS $protobuf_CFLAGS"

t/test-full.proto

@@ -45,6 +45,7 @@ enum TestEnumDupValues {
   VALUE_F = 1000;
   VALUE_AA = 1000;
   VALUE_BB = 1001;
+  option allow_alias = true;
 }
 
 message TestFieldNo15 {			// should use 1 byte header