Change the default value for Re-record watched setting.

Since more and more users are trusting auto-expire to delete shows
(whether using "Auto-Expire instead of delete recording" or just letting
MythTV expire shows when file systems fill), it now makes sense for the
"Re-record watched" setting to default to disabled.  And since
"Automatically mark a recording as watched" defaults to disabled, by
default, this will only affect shows the user manually marks as watched.

Several times users have appeared in IRC or on list asking why MythTV is
re-recording shows they'd already recorded and watched, and are finding
out that because they had left "Re-record watched" enabled, all the
shows that were auto-expired since they started using MythTV will be
re-recorded when they re-air.  Therefore, this changes the default so
that only shows not marked watched will be re-recorded.

This does not affect existing installations of MythTV.  For those users
who see this change and decide to manually change the "Re-record
watched" setting on their systems, doing so will have no effect on
whether shows that were previously auto-expired will be re-recorded--it
only affects shows as they are being expired.  Users wanting to prevent
re-record of shows that were previously expired and set to allow
re-record will need to use Manage Recordings|Previously Recorded to set
the episodes to "Never record this episode."

mythtv/programs/mythfrontend/globalsettings.cpp

@@ -467,7 +467,7 @@ static GlobalCheckBox *RerecordWatched()
 {
     GlobalCheckBox *bc = new GlobalCheckBox("RerecordWatched");
     bc->setLabel(QObject::tr("Re-record watched"));
-    bc->setValue(true);
+    bc->setValue(false);
     bc->setHelpText(QObject::tr("If enabled, programs that have been marked as "
                     "watched and are Auto-Expired will be re-recorded if "
                     "they are shown again."));