Add support for default enum values that reference the original enum.

[mikekap]

e.g. 1: PhoneType phone_type = PhoneType.MOBILE;

[hit9]

LGTM

[lxyu]

Thanks!

[hit9]

@mikekap Is the following legal?

struct Person {
    1: string name,
    2: i32 age
    3: Country country = Country.US
}

enum Country {
    US = 1,
    UK = 2,
    CA = 3,
}

I mean when the referenced enum is defined after the referencer (here 'struct Person').

[hit9]

I have tested the following thrift file:

struct Person {
    1: Country country = Country.US
}

enum Country {
    US = 1
}

Apache thrift gives out:

[ERROR:/Users/hit9/spam/testth/hello.thrift:2] (last token was 'Country')
Type "Country" has not been defined.

[hit9]

So, we should replace the real value in the ply parsing progress.

[hit9]

Parser has been rebuilt, but this feature was included.