Add support for SSH_ASKPASS_ALWAYS env variable for dbclient. If it

(and also SSH_ASKPASS) is set then dbclient will use an external askpass
program regardless of whether DISPLAY is set or stdin is a TTY. Suggested
by Davyd Madeley for handheld devices.

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extra : convert_revision : c62bdee8427eb452cca38d188affe881d9fadee8