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