logilab-database #83603 sql server lacks sql_current_date and al. [validation pending]

the sql_current_date and others from the base helper don't work for sql server.

and the GETDATE function cannot be used in substituted parameters.

priorityimportant
typebug
done in1.8.1
load left0.000
closed by#b944d435426b provide implementation of sql_current_date|timestamp for sql serve (closes #83603)