BUG #11944: plpgsql if-case-then syntax error.

The following bug has been logged on the website:

Bug reference:      11944
Logged by:          Jasen Betts
Email address:      jasen@treshna.com
PostgreSQL version: 9.1.13
Operating system:   linux
Description:

this does work

create function fails( a int) returns int language plpgsql as $$ begin
  if  CASE when a = 1 then true else false END
  then return 1; else  return 0;  end if ;
end $$;

parentheses can make it work.

create function fails_not( a int) returns int language plpgsql as $$ begin
  if ( CASE when a = 1 then true else false END )
  then return 1; else  return 0;  end if ;
end $$;

It seems to be the plpgsql parser not treating the CASE-END as atomic when
looking for the end of the IF xpression.