(sql-ms): Added autoload cookie.

(sql-ms): Added autoload cookie.
(sql-ingres, sql-solid, sql-mysql, sql-informix, sql-sybase)
(sql-oracle): Ditto.
(sql-help): Doc change.

(sql-mode-oracle-font-lock-keywords): Added PL/SQL keywords, data
types and exceptions.

(sql-placeholder-history): New variable.
(sql-query-placeholders-and-send): New function that will query
the user and replace placeholders with user input.
(sql-oracle): If running on NT, set comint-input-sender to
sql-query-placeholders-and-send.

(sql-stop): If in the SQLi buffer, insert stop notification, else
present it as a message.

(sql-input-ring-separator): Doc change.
(sql-input-ring-file-name): Doc change.
(sql-interactive-mode): Use `sql-input-ring-separator' and
`sql-input-ring-file-name' to set the comint-mode equivalents
without making them local variables.
(sql-stop): Don't bind `sql-input-ring-separator' and
`sql-input-ring-file-name' dynamically to their comint-mode
equivalents.