Fix Issues #82 - Disable builtins for browserify

Closes #82
```
client/src/index.js:var Filer = require('filer');
lib/diff.js: var Buffer = require('filer').Buffer;
lib/rsync.js:var Filer = require('filer'),
server/lib/filer-www.js:var Path = require('filer').Path;
tests/lib/util.js:var Buffer = require('filer').Buffer;
tests/unit/rsync-tests.js:var Filer = require('filer'),
tests/unit/util-tests.js:var FileSystem = require('filer').FileSystem;
```
Everywhere that we `require('filer')` we just need to change it to `require('./path/to/thirdparty/filer/src')`.  You should fix that in here too.