Transitive inclusion path should not walk the full directory structure

Let us that __project A__ has the following file:
src/main/thrift/com/example/a.thrift
Assume we have generated a jar using this plugin on project A

Our project (say project B) depends on a.thrift. The way to accomplish
this is by declaring the maven artifact of project A as a dependency in
our project and then referencing the file as follows:

```thrift
// contents of com/acme/b.thrift
include "com/example/a.thrift"
```

Now, when the plugin is invoked, the expected behaviour is as follows:
* a.thrift gets unpacked into a temp directory as temp/hashcode/com/example/a.thrift
* the thrift executable is called on com/acme/b.thrift with the correct include paths

The curent implementation passes _temp/hashcode/com/example/_ as an
include base directory. The issue with this approach is that the fully
qualified reference that exists in b.thrift does not get resolved. The
correct approach is to set _temp/hashcode/_ as the include directory.
Note that this change has no effect on dependencies where the IDL files
are placed only in the source root i.e. they are not placed inside
sub-directories