There should be one instance of tool per image

[janisozaur]

Currently, there is only one, global, tool instance per one carto instance.
This is bad, as in a threaded solution implemented recently one thread has to paint on multiple images simultaneously and it is not only counterproductive, but also complex and cumbersome to implement. Due to this, after creating second image and trying to paint in it, carto crashes.
You can verify this issue by inspecting output from http://bazaar.launchpad.net/%7Ecarto-team/cybercarto/carto/annotate/head%3A/paintarea.cpp#L459.
There should be one instance of tool (thread) per image, they can share settings, though.

[janisozaur (janisozaur)]

duplicated in bug 636377

[janisozaur (janisozaur)]

The commited fix is sort of a workaround - it stores the read/write thread client and host, respectively, indices in image. This lets us to avoid aforementioned problems at the expense of painting on only one image at any given time (i.e. there is no possibility of any deferred actions, as they might get lost).