pgsql: Do stack-depth checking in all postmaster children.

Do stack-depth checking in all postmaster children.

We used to only initialize the stack base pointer when starting up a regular
backend, not in other processes. In particular, autovacuum workers can run
arbitrary user code, and without stack-depth checking, infinite recursion
in e.g an index expression will bring down the whole cluster.

The comment about PL/Java using set_stack_base() is not yet true. As the
code stands, PL/java still modifies the stack_base_ptr variable directly.
However, it's been discussed in the PL/Java mailing list that it should be
changed to use the function, because PL/Java is currently oblivious to the
register stack used on Itanium. There's another issues with PL/Java, namely
that the stack base pointer it sets is not really the base of the stack, it
could be something close to the bottom of the stack. That's a separate issue
that might need some further changes to this code, but that's a different
story.

Backpatch to all supported releases.

Branch
------
REL8_3_STABLE

Details
-------
http://git.postgresql.org/pg/commitdiff/ddeac5dec10abe8b26d6a336f95ca593dcf3f3df

Modified Files
--------------
src/backend/postmaster/postmaster.c |   11 ++++++
src/backend/tcop/postgres.c         |   61 ++++++++++++++++++++++++++++++----
src/include/miscadmin.h             |   13 +++++++
3 files changed, 77 insertions(+), 8 deletions(-)