Incorrect START TRANSACTION implementation

SQL99 part 2 clause 16.1 contains this note:
   NOTE 327 - The characteristics of a transaction begun by a   <start transaction statement> are as specified in these
General  Rules regardless of the characteristics specified by any   preceding <set transaction statement>. That is,
evenif one   or more characteristics are omitted by the <start transaction   statement>, the defaults specified in the
SyntaxRules of this   Subclause are effective and are not affected by any (preceding)   <set transaction statement>.
 

In other words, this should work:

peter=# set session characteristics as transaction read only;
SET
peter=# start transaction;
START TRANSACTION
peter=# create table test (a int);
ERROR:  transaction is read-only

because the default of a bare "start transaction" is read write.  I 
propose that we change this to follow the standard and keep the 
traditional behavior for BEGIN only.