Leading '.' not supported

test.proto
```proto
enum FOO {
BAR = 1;
}
message AnotherOne {
.FOO list = 1;
}
```
```js
> var messages = protobuf(fs.readFileSync('test.proto'))
Uncaught Error: Could not resolve .FOO
```
See https://developers.google.com/protocol-buffers/docs/proto#packages-and-name-resolution:
> Type name resolution in the protocol buffer language works like C++: first the innermost scope is searched, then the next-innermost, and so on, with each package considered to be "inner" to its parent package. **A leading '.' (for example, .foo.bar.Baz) means to start from the outermost scope instead.**

Start by reproducing the example from test.proto with the JavaScript protobuf(fs.readFileSync('test.proto')) entry point. Compare the resolver's behavior with the linked Protocol Buffers name-resolution rules. Done means a leading-dot type such as .FOO resolves from the outermost scope without the reported error.

Written by the indexing model from the issue text.