alter sql.php prompt on line continuation

alter sql.php prompt on line continuation

As long as a command is not ended with a database delimiter, sql.php
kept appending the line without noticing the users. That is a bit
confusing since you might not even know what you are going to run when
entering the delimiter.

This patch alter the prompt to '    ->' until the command is finished.
That is more in line with how MySQL cli handles it.

Example:
	$ php sql.php
	> SELECT
		-> *
		-> from
		-> job;
	Query OK, 0 row(s) affected
// repeal command:
	> SELECT * from job

Change-Id: Ic18b39d75d4db48d37d485e66f36d691e95934fb