update_fix_d7_block_deltas() helper function broken for non-core modules

the recently added update_fix_d7_block_deltas() helper function currently bombs if it's used any time after block_update_7002().

this is because that update changes the block table names, and the helper function was written for the old table names (which are what's used when the block delta settings for the core modules are updated).

so this means that the function works fine for the core block delta upgrades, but is totally busted if any contrib tries to use it. not a very useful helper function ;)

attached patch adds a simple check for which set of table names the function is dealing with, and uses the appropriate set. tested and works for both the core delta updates, and a contrib delta update.

apologies for not catching this in my original patch to create the helper -- at the time i couldn't test the contrib module update b/c core's update process was so broken!