Use godep for dependencies with vendored source




Install godep:

```
  go get github.com/tools/godep
```

The initial dependency list was generated using the following command:

```
  godep save
```

However, this dependency list used the latest version of cloudwatch.  I edited the version SHA in the Godeps.json file to a known good version:

 [ bfa553e3b7d6416a36cb81ff5f379acfb9b93f0d](https://github.com/crowdmob/goamz/commit/bfa553e3b7d6416a36cb81ff5f379acfb9b93f0d)

Using these verisons of the library, the ones specified in the Godeps.json file, I was able to build pdfcombiner using:

```
  godep go build
```