Log Message:
Update skkinput to 2.06.4.
Based on patch provided by Ryo ONODERA in PR 42416 (include user-destdir support).
While here set LICENSE=gnu-gpl-v2.

* 2.06.3 -> 2.06.4
 - close IM by Shift-Space even if NumLock or CapsLock.
 - fix skkinput.ja.man install path