node update saves block settings to all themes

the update of the blocks table in nodeasblock_save_block() doesn't have a theme qualifier, so it's putting the region, pages, etc information selected on the node edit form into the blocks rows for all the themes in the installation. i notice this mostly because i use a different theme for administration and am getting "invalid region" warnings about the node blocks.

i copied the code from _nodeasblock_node_form() that selects a theme to use for generating the available regions list, and that seems to fix the problem. i don't know if the init_theme() call is necessary here or not, though.