pgsql: Add simple script to check for right recursion in Bison grammars

Add simple script to check for right recursion in Bison grammars.

We should generally use left-recursion not right-recursion to parse lists.
Bison hasn't got any built-in way to check for this type of inefficiency,
and I didn't find anything on the net in a quick search, so I wrote a
little Perl script to do it. Add to src/tools/ so we don't have to
re-invent this wheel next time we wonder if we're doing anything stupid.

Currently, the only place that seems to need fixing is plpgsql's stmt_else
production, so the problem doesn't appear to be common enough to warrant
trying to include such a test in our standard build process. If we did
want to do that, we'd need a way to ignore some false positives, such as
a_expr := '-' a_expr

Branch
------
master

Details
-------
http://git.postgresql.org/pg/commitdiff/756a4ed5ad3e57c26a247234de371a6ca21806cd

Modified Files
--------------
src/tools/check_bison_recursion.pl | 74 ++++++++++++++++++++++++++++++++++++
1 files changed, 74 insertions(+), 0 deletions(-)