[mythtv] Improve server reconnect/wakeup method

[Matthew Wire]

Please take a look at http://svn.mythtv.org/trac/ticket/3279

This patch improves the server reconnect attempt used in mythcontext.

A mythbusydialog is displayed while myth is trying to connect rather
than just appearing with a blank background and a log message (dialog is
disabled when a mythcontext server connection is made without a gui -
eg. with mythshutdown).

The reconnect algorithm is adjusted such that:
1. Wakeup command is executed.
2. Myth attempts to open a connection to the backend once every second
until the reconnect timeout occurs or a connection is established.
3. If the reconnect timeout is reached, the wakeup command will be
issued again (as before), unless the max number of attempts have been
executed.

This is more efficient than before, where the reconnect attempt would
not retry until the next wake command is executed.