THRIFT-2543 Generated enum type in haskell should be qualified

Compile following thrift files
**a.thrift**
```thrift
enum X {
  A = 1,
  B = 2,
  C = 4,
  D = 8
}
```

**b.thrift**
```thrift
include "a.thrift"

struct B {
  1: a.X x;
  2: i32 y;
}
```

In generated haskell file, we find
**B_Types.hs**
```haskell
import qualified A_Types

data B = B{f_B_x :: Maybe X,f_B_y :: Maybe Int32} deriving (Show,Eq,Typeable)
```

It should be
**B_Types.hs**
```haskell
import qualified A_Types

data B = B{f_B_x :: Maybe A_Types.X,f_B_y :: Maybe Int32} deriving (Show,Eq,Typeable)
```