commitmonitor Code

Ensure the selected item is visible when navigating with 'n' or 'b'.
This adds to issue #89.

Fixed issue #89: Navigating with key 'n' doesn't work
If no more unread items are available, 'n' goes to the next item.

Bugfix: Clicking on the "Show Diff" button did not respect the setting "Use TortoiseSVN for showing diffs" but always unconditionally used TortoiseSVN.

Additionally: Two functions (OnDblClickListItem and DoCommand) which interpreted the setting have been refactored to use the new ID_MAIN_SHOWDIFFCHOOSE command.

Add an update notification if a newer version of the CommitMonitor is available.

Implemented issue #72: Add fourth column showing start of commit message

Use the new utility function to find out the installation path of TortoiseSVN.
This solves issue #80.

Add keyboard shortcuts:
N : go to the next unread item. If there are no more unread items in the currently selected project, move to the next project which has unread items.
B : goes back one message

Implements part of issue #73: Keyboard shortcuts

Check whether the focus in on the OK/Hide button when ENTER is pressed; only close the dialog if the focus is there.
If the focus is on the list control, execute the diff (default action of the context menu).

This fixes issue #77: Pressing "enter" unexpectedly closes "Commit Monitor" application window

Show the time the selected repository was last checked in the info label at the bottom left.
This implements the suggestion in issue #68.

Prevent selecting an entry when doubleclicking on the error text shown over the list control.
This fixes issue #68.