Log Message:
Update mikutter to 3.5.6.

Upstream changes:

mikutter 3.5.6

* crash when icons for extract tabs could not be accessed (thanks ahiru3net)
* remove unused code (thanks ahiru3net)
* support files with .jpeg extentions in image viewer (thanks moguno)
* change timing of argument evaluation on startup (thanks ahiru3net)
* fix warnings (thanks ahiru3net)