Memory allocation abstraction in pgcrypto

pgcrypto has an abstraction for palloc/pfree via PX_OWN_ALLOC with the
intention to make it easy to swap out for another allocator. There are however
a number of palloc calls that have snuck in over the years, so the abstraction
is leaking a fair bit making it less useful. Since there have been no
complaints that I can see (searching the archives for PX_OWN_ALLOC yields zero
threads, and px_alloc none about this topic) then maybe it's time to remove it
and simplify the code?

The attached removes it in favor of using palloc() et.al directly. Is there
any reason to keep it around still?

cheers ./daniel