tests: use filepaths directly

After a long IRC discussion, it was decided that the use of direct
filepaths instead of the module is a more pure form of testing ,
although it may provide less overall coverage than the mixed integration
style imports used previously.

This will need to be remedied by further integration testing in
/test/integration.

test/message.js

@@ -1,8 +1,8 @@
 var assert = require('assert')
-var networks = require('..').networks
+var networks = require('../src/networks')
 
-var ECKey = require('..').ECKey
-var Message = require('..').Message
+var ECKey = require('../src/eckey')
+var Message = require('../src/message')
 
 var fixtures = require('./fixtures/message')