Add EUC-JP-2004 as alias of EUC-JP

Merge CRuby r35460.
Use ENC_DUMMY_UNICODE for UTF-16 and UTF-32

Merge CRuby r37101.
The name "ENC_DUMMY_UNICODE" indicates to CRuby that it is an encoding
of Unicode family in pre-compile process of CRuby encoding build process.
For more detail, inspect CRuby's build process of encdb.h and enc/encdb.c.
Merge pull request #10 from nurse/cruby-r35460-r37101

Cruby r35460 r37101