Recompile curve25519 with emcc 1.29.0

Now with actual malloc/free implementations. Had to drop back to -O1
optimization because the ed25519 signature test broke with -O2. :(

Closes #153

The toolchain install and build process, for reference:
```
wget https://s3.amazonaws.com/mozilla-games/emscripten/releases/emsdk-portable.tar.gz
tar xvfz emsdk-portable.tar.gz
cd emsdk-portable
./emsdk update
./emsdk install latest
./emsdk activate latest
source ./emsdk_env.sh
cd ../TextSecure-Browser
grunt build
```

Gruntfile.js

@@ -233,7 +233,7 @@ module.exports = function(grunt) {
         return "'_" + name + "'";
       });
       var flags = [
-          '-O2',
+          '-O1',
           '-Qunused-arguments',
           '-o',  outfile,
           '-Inative/ed25519/nacl_includes -Inative/ed25519 -Inative/ed25519/sha512',