[TYPO3-core] RFC #10891: Bug: Page caching with external files enabled fails if files are not found.

[Vahan Amirbekyan]

This is an SVN patch request

Type: New feature
Bugtracker references: http://bugs.typo3.org/view.php?id=10891
Branches: 4.2.2

Problem: Page caching with external files enabled fails if files are not 
found.

Solution: With [FE][pageCacheToExternalFiles] = 1 if files are not found 
blank pages been rendered.
A patch is needed for failover scenarios then traffic is redirected to a 
different server where files do not exist.
The patch simply invalidates the cache record and as result the pages 
gets re-cached.