Move many includes down to the EXITFREE block.

They're unnecessary for the rest of the file, and they're only there at
all to help implement `free_all_mem` for use with Clang's Address
Sanitizer.  So let's move them to avoid any confusion about why they are
there.
Merge pull request #1439 from jszakmeister/shuffle-some-includes

Move many includes down to the EXITFREE block.