Fix os x build again by adding variable LIBPROTOBUF=/usr/local/Cellar/protobuf/2.5.0

OS X build fail without this...

$ brew install protobuf
Warning: It appears you have MacPorts or Fink installed.
Software installed with other package managers causes known problems for
Homebrew. If a formula fails to build, uninstall MacPorts/Fink and try again.
==> Downloading http://protobuf.googlecode.com/files/protobuf-2.5.0.tar.bz2
######################################################################## 100.0%
==> ./configure --prefix=/usr/local/Cellar/protobuf/2.5.0 --with-zlib
==> make
==> make install
==> Caveats
Editor support and examples have been installed to:
  /usr/local/Cellar/protobuf/2.5.0/share/doc/protobuf
==> Summary
/usr/local/Cellar/protobuf/2.5.0: 75 files, 6.2M, built in 84 seconds

$ npm install node-protobuf
npm http GET https://registry.npmjs.org/node-protobuf
npm http 304 https://registry.npmjs.org/node-protobuf

> node-protobuf@1.0.10 install /Users/h0x91b/Desktop/ESBZmq/node_modules/node-protobuf
> node-gyp rebuild

  CXX(target) Release/obj.target/protobuf/protobuf.o
../protobuf.cpp:7:10: fatal error: 'google/protobuf/dynamic_message.h' file not found
#include <google/protobuf/dynamic_message.h>
         ^
1 error generated.
make: *** [Release/obj.target/protobuf/protobuf.o] Error 1
gyp ERR! build error 
gyp ERR! stack Error: `make` failed with exit code: 2
gyp ERR! stack     at ChildProcess.onExit (/opt/local/lib/node_modules/node-gyp/lib/build.js:267:23)
gyp ERR! stack     at ChildProcess.EventEmitter.emit (events.js:96:17)
gyp ERR! stack     at Process._handle.onexit (child_process.js:678:10)
gyp ERR! System Darwin 13.0.0
gyp ERR! command "node" "/opt/local/bin/node-gyp" "rebuild"
gyp ERR! cwd /Users/h0x91b/Desktop/ESBZmq/node_modules/node-protobuf
gyp ERR! node -v v0.8.11
gyp ERR! node-gyp -v v0.12.1
gyp ERR! not ok 
npm ERR! node-protobuf@1.0.10 install: `node-gyp rebuild`
npm ERR! `sh "-c" "node-gyp rebuild"` failed with 1
npm ERR! 
npm ERR! Failed at the node-protobuf@1.0.10 install script.
npm ERR! This is most likely a problem with the node-protobuf package,
npm ERR! not with npm itself.
npm ERR! Tell the author that this fails on your system:
npm ERR!     node-gyp rebuild
npm ERR! You can get their info via:
npm ERR!     npm owner ls node-protobuf
npm ERR! There is likely additional logging output above.

npm ERR! System Darwin 13.0.0
npm ERR! command "node" "/usr/local/bin/npm" "install" "node-protobuf"
npm ERR! cwd /Users/h0x91b/Desktop/ESBZmq
npm ERR! node -v v0.8.11
npm ERR! npm -v 1.1.62
npm ERR! code ELIFECYCLE
npm ERR! 
npm ERR! Additional logging details can be found in:
npm ERR!     /Users/h0x91b/Desktop/ESBZmq/npm-debug.log
npm ERR! not ok code 0