mg-desktop: SetResource does not flush out cached resource content

[jng]

For mg-desktop's implemented MgResourceService, we keep an in-memory cache of any resource content to avoid hitting the hard disk every time for resource content.

However, flushing out the in-memory cached version of the resource if it exists only happens on a DeleteResource() call. Thus, doing a SetResource() call on a resource already cached and doing a subsequent GetResourceContent() will still retrieve the old cached version.

We have a hook function ReleasePotentialLocks() that does all flushing of any cached objects associated with a given resource. We should also flush any in-memory resource content here as well.

[jng]

Fixed 2.5 (r7531) and trunk (r7540)