[BUGFIX] Fix uid_local out of range error when using workspaces

[maechler]

We get the following error using workspaces together with EXT:blog when we try to publish a blog post:

An exception occurred while executing 'UPDATE `tx_blog_post_author_mm` SET `uid_local` = ? WHERE `uid_local` = ?' with params [-2541, 2541]: Out of range value for column 'uid_local' at row 1

The problem seems to be that the column uid_local does only allow unsigned integers, the workspace extension however tries to set it to a negative value. To fix this I simply used the column definitions from tx_blog_tag_pages_mm.