syntax extension for unsupported JOINs coming from a binary only (unmodifyable) program

Here are some little changes to the postgreSQL server backend I found
beeing convenient for me
while I was attempting to get interoparability with a binary only
program. The patch attached is tested and works
for 8.0.0beta3.
The so called big ones under these DBMS eat the following kind of join
without complaining:

select a.val1, b.val2, c.val3 from
    t1 a left outer join t2 b on (a.id1=b.id2),
    t1    left outer join t3 c on (a.id1=c.id3);

the content of the patch reorders the parse tree to get the same result
as this (working recursively for subselects etc.):

select a.val1, b.val2, c.val3 from
    t1 a left outer join t2 b on (a.id1=b.id2)
    left outer join t3 c on (a.id1=c.id3);

Wolfgang