WL#930: Allow -- comments with no space

MySQL, like Sybase, requires that simple comments 
begin with "-- " and not merely "--" to avoid 
ambiguity. But following the suggestion of Mr Åke 
Persson from that other Uppsala DBMS company, there 
will be a change to SQL:2003 which solves the 
ambiguity in a different way. The numeric 
expression "x--5" will be illegal but "x- -5" will 
be valid. 
 
SQL:2003 and SQL:2008 now say:
"
<simple comment> ::=
   <simple comment introducer> [ <comment character>... ] <newline>
<simple comment introducer> ::=
   <minus sign><minus sign>
...
There shall be no <separator> separating the <minus sign>s of a <simple comment
introducer>.
...
<newline> is the implementation-defined end-of-line indicator
...
if [string used in PREPARE] contains a <simple comment> then an
exception condition is raised: syntax error or access rule violation.
...
"

Presumably we would define end-of-string as a type of <newline>.

This is a behaviour change and I think Monty doesn't like it much.
But if we start by deprecating the old behaviour in MySQL 6.x,
I think it should be safe to get this into 7.x.

Feature requests:
BUG#14032 Comment with space requirement '-- ' is not standard SQL 92