Upgrade hook_block_info()

So, this is mostly working in master now. I ran it on the D7 core modules directory, and it more-or-less successfully created block plugins from the following modules' hook_block_info() implementations:
user
shortcut
search
profile
poll
node
forum
comment
book
blog

It adds non-fixable errors for the following modules' implementations, all of which contain logic (e.g. foreach loops that would need to be converted to block derivatives):
system
statistics
menu
locale
block_test
block
aggregator

There are a few outstanding bugs, but I'll file them in their own issues.