Fix potential infinite loop in CDB_QueryStatements

This fix was already present at one point in cartodb/lib/sql
(where the code was copied from) but in a different branch than
the one the code was initially copied from.

The fix depends on plpython language which becomes a new dependency.

test/CDB_QueryStatementsTest.sql

@@ -26,3 +26,38 @@ INSER INTO "my''""t" values ('''','""'';;');
 SELECT $qu;oted$ hi $qu;oted$;
 $the_param$) as statement )
 SELECT '5', row_number() over (), statement FROM q;
+
+WITH q AS ( SELECT CDB_QueryStatements($the_param$
+SELECT
+1 ; SELECT
+2
+$the_param$) as statement )
+SELECT '6', row_number() over (), statement FROM q;
+
+-- This is an insane input, illegal sql
+-- we are really only testing that it does not
+-- take forever to process..
+-- The actual result is not correct, so if the function
+-- ever gets fixed check if it's better
+WITH q AS ( SELECT CDB_QueryStatements($the_param$
+
+
+
+
+
+
+
+
+    /a
+    $b$
+    $c$d
+    ;
+$the_param$) as statement )
+SELECT '7', row_number() over (), statement FROM q;
+
+
+WITH q AS ( SELECT CDB_QueryStatements($the_param$
+SELECT $quoted$ hi
+$quoted$;
+$the_param$) as statement )
+SELECT '8', row_number() over (), statement FROM q;