[gthumb-list] Merge branch 'ext'

[Paolo Bacchilega <paolo bacchilega libero it>]

Hello,

I've merged the ext branch in master and will do a 2.11.1 release very 
soon (Monday or Tuesday).

The ext branch still lacks some useful features like the web album 
exporter, but at this point it's important to do a release to get some 
feedback from the users, the current master branch will be copied in the 
'gthumb-2-11-old' branch for reference to fix regressions.

- Paolo