Replace use malloc() & friend by memory contexts for plperl and pltcl

Hi all,

Cleanup $subject has been raised a couple of times, like one year ago here:
https://www.postgresql.org/message-id/CAB7nPqRxvq+Q66UFzD9wa5UAftYN4WAUADbjXKFrync96kf-VQ@mail.gmail.com
And more recently here while working on the NULL checks for malloc():
https://www.postgresql.org/message-id/CAB7nPqR7ozfCqc6C=2+ctCcnuehTZ-vTDQ8MMhY=BQyET0Honw@mail.gmail.com

Attached are a set of patches to replace those memory system calls by
proper memory contexts:
- 0001 does the cleanup work for pltcl
- 0002 does this cleanup for plperl

Thoughts?
--
Michael