Validate command on toolbar should be validating resource of active editor

[jng]

In an oversight that was not apparent until now, the validate command on the toolbar does not actually validate the resource of the active editor (as some, including myself would've believed). The current command is actually the same validate context menu command, meaning it will validate the selected items on the Site Explorer.

A separate validate command should be defined that does this validation and the existing toolbar command should be replaced with this one.

[jng]

Fixed r5723