fix continual wakeups with miniview every 0.1 sec

as pointed out by GKH:

https://plus.google.com/u/0/111049168280159033135/posts
extns: Add .tga to the recognized image files

Add it to tyls as well
Miniview: Fix crash due to miniview render after deletion

_deferred_renderer() could be called after object del because the
timer was renewed even though it was invalid (marked as NULL).
hide tw popup on terminal popup show

fix T1290
disallow tw popups while terminology popup is present

fix T1290
fix possible segfault detected as CID1224396.
Terminology 0.6.1