Prompt before upgrading database schema

[Nigel]

This adds a new method, MythContext::PromptForSchemaUpgrade() which if possible asks the user before upgrading the database schema. If the context has a GUI (mythtv-setup, mythfrontend) it will use a Popup. If the context has no GUI (mythbackend and friends), it prompts in the command shell (unless stdin or stdout is redirected, in which case it defaults to the current behaviour - upgrading).

If the user/developer wants to always live dangerously, set DBSchemaAutoUpgrade in the database.

The patch enables this for TV database schema upgrades only, but it could also be added to plugins.

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Please test. Bug reports, better warning messages or button labels are all very welcome.
I would like to add this soon, before too many UPnP autodiscovery testers wreck their backends :-)

[Nigel]

(In [14562]) Use defaults for user response from non-interactive shells. Only currently used when prompting for database params (mysql.txt), but schema upgrading will also use it in the future (see #4013).

[Nigel]

Expert mode for "Use existing", confirmation prompting, check for newer schema

[Nigel]

(In [14673]) Prompt for database schema upgrades. Closes #4013. Doesn't check for multiple clients connected to the backend yet.

[stev391]

My backend refused to automatically update the database schema. It defaulted to no when queried to continue when stating that a database backup should be performed. It did default to yes to the first question. It took my ssh session as a none interactive console and would not let me input values. I had to run an X session without the frontend to run mythtv-setup to confirm that I wanted it to update.

This is what it stated (with or without interactive console) without any verbose commands: 2007-10-14 20:39:55.511 Using runtime prefix = /usr 2007-10-14 20:39:55.537 New DB connection, total: 1 2007-10-14 20:39:55.541 Connected to database 'mythconverg' at host: localhost 2007-10-14 20:39:55.543 Current Schema Version: 1199

Warning: MythTV wants to upgrade your database schema, from 1199 to 1200.

Shall I upgrade this database? [yes] [console is not interactive, using default 'yes']

A database backup might be a good idea Are you sure you want to upgrade? [no] [console is not interactive, using default 'no'] 2007-10-14 20:39:55.549 Couldn't upgrade database to new schema 2007-10-14 20:40:02.36 /root/bin/mythmon: mythbackend not running!!! 2007-10-14 20:50:01.202 /root/bin/mythmon: mythbackend not running!!!

[Nigel]

(In [14685]) For non-interactive shells, always default to upgrading the database schema (i.e. original behaviour). I wish there was a simple way to detect interactive shells that works for ssh, but the amount of code isn't worth it. See #4013