versionCache is not cleaned when a subwiki is deleted, making it impossible to recreate a subwiki with the same name.

How to reproduce the effects:
1. Go to the WikiManager/CreateNewWiki page and create a simple (empty) wiki named 'testdoublecreation'
2. After it finishes to be created, go to WikiManager/WebHome and delete the just created wiki
3. Repeat step 1

You will see an error like:

Wiki "testdoublecreation" creation failed: Error number 50035 in 5: Exception in plugin xpn.xwiki.plugin.wikimanager.Wiki Manager Plugin?: Wiki testdoublecreation? database update failed Wrapped Exception: Error number 3202 in 3: Exception while reading document name = [XWiki Preferences?, type = DOCUMENT?, parent = name = [XWiki?, type = SPACE?, parent = name = [testdoublecreation?, type = WIKI?, parent = null?]]] Wrapped Exception: could not load an entity: xpn.xwiki.doc.XWiki Document?.

Workaround:

Restart XWiki and the in-memory caches will be cleared so the subwiki can be again created.

Technical details:

The version check will only be null the first time the subwiki is created:
AbstractDataMigrationManager.java

The next times it will always be found in the versionCache because the version cache is never cleared on wiki deletion:
XWikiCacheStore.java #flushCache()
– called by:
XWikiCacheStore.java #deleteWiki()
XWikiCacheStore.java #onEvent() <- triggered by com.xpn.xwiki.plugin.wikimanager.doc.Wiki#delete()

Maybe a solution would be to make AbstractDataMigrationManager implement EventListener and listen to WikiDeletedEvent. Then, on the event, it could set the versionCache key corresponding to the just deleted wiki to null.