pgsql: Detect mismatched CONTINUE and EXIT statements at plpgsql compil

Detect mismatched CONTINUE and EXIT statements at plpgsql compile time.

With a bit of tweaking of the compile namestack data structure, we can
verify at compile time whether a CONTINUE or EXIT is legal.  This is
surely better than leaving it to runtime, both because earlier is better
and because we can issue a proper error pointer.  Also, we can get rid
of the ad-hoc old way of detecting the problem, which only took care of
CONTINUE not EXIT.

Jim Nasby, adjusted a bit by me

Branch
------
master

Details
-------
http://git.postgresql.org/pg/commitdiff/fcdfce6820373422bcdb5630f9eb63df14fd0764

Modified Files
--------------
src/pl/plpgsql/src/pl_comp.c          |    4 +-
src/pl/plpgsql/src/pl_exec.c          |   48 ++++---------------
src/pl/plpgsql/src/pl_funcs.c         |   23 ++++++++-
src/pl/plpgsql/src/pl_gram.y          |   70 ++++++++++++++++++++++-----
src/pl/plpgsql/src/plpgsql.h          |   17 ++++++-
src/test/regress/expected/plpgsql.out |   85 ++++++++++++++++++++++++++-------
src/test/regress/sql/plpgsql.sql      |   64 ++++++++++++++++++++-----
7 files changed, 226 insertions(+), 85 deletions(-)