Update protobuf library from 2.3 to 2.6.

Copied in all files from the open source protobuf project at commit
edc5994525c79cd1919859a370837a6ff7c8e308, removing files which have
been renamed (COPYING.txt -> LICENSE, README.txt -> README.md).

Removed 2.3 prebuilts, which is an approach that will not work due to
incompatibility with the 2.6 runtime.

Merged in micro/nano-specific changes in the following files:

-Android.mk - updated list of C++/Java sources, bumped versions
-java/README.txt - merged in micro/nano instructions, bumped versions
-java/pom.xml - merged in micro/nano build rules, set packaging to jar
-src/Makefile.am - merged in references to micro/nano generators
-src/google/protobuf/compiler/javamicro/javamicro_file.h - imported
 google/protobuf/compiler/code_generator.h and removed redundant
 OutputDirectory class.
-src/google/protobuf/compiler/javanano/javanano_file.h - same
-Replaced instances of vector with std::vector as needed to get
 libprotobuf-cpp-full to compile. Plan to upstream this fix per
 discussion with protobuf maintainers.

Reran autogen.sh to update ./configure and associated scripts.

Change-Id: I949d32fb5126f1c05e2a6ed48f6636a4a9b15a48
diff --git a/build.gradle b/build.gradle
index 95c9b1d..4684592 100644
--- a/build.gradle
+++ b/build.gradle
@@ -55,7 +55,7 @@
     from sourceSets.nano.output, sourceSets.micro.output
     baseName "libprotobuf"
     appendix "java"
-    version "2.3"
+    version "2.6"
     classifier "micronano"
 }
 
@@ -64,7 +64,7 @@
     dependsOn nanoClasses
     baseName "libprotobuf"
     appendix "java"
-    version "2.3"
+    version "2.6"
     classifier "nano"
 }
 
@@ -73,7 +73,7 @@
     dependsOn microClasses
     baseName "libprotobuf"
     appendix "java"
-    version "2.3"
+    version "2.6"
     classifier "micro"
 }