pgsql: Fix (some of) pltcl memory usage

Fix (some of) pltcl memory usage

As reported by Bill Parker, PL/Tcl did not validate some malloc() calls
against NULL return. Fix by using palloc() in a new long-lived memory
context instead. This allows us to simplify error handling too, by
simply deleting the memory context instead of doing retail frees.

There's still a lot that could be done to improve PL/Tcl's memory
handling ...

This is pretty ancient, so backpatch all the way back.

Author: Michael Paquier and Álvaro Herrera
Discussion: https://www.postgresql.org/message-id/CAFrbyQwyLDYXfBOhPfoBGqnvuZO_Y90YgqFM11T2jvnxjLFmqw@mail.gmail.com

Branch
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REL9_2_STABLE

Details
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http://git.postgresql.org/pg/commitdiff/3cb6ef9983b5d7b45e7a5bd42c2cf8714f931850

Modified Files
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src/pl/tcl/pltcl.c | 27 ++++++++++++++++++---------
1 file changed, 18 insertions(+), 9 deletions(-)