Problem after recursively deleting content and then trying to add new content

[benhj]

Strange behaviour; steps to reproduce --

(i) recursively copy content to a newly created image
(ii) recursively delete it,
(iii) create a new sub folder
(iv) cd into the new sub folder.
(v) attempt to recursively copy content in to the newly created sub folder

Step (v) results in a freeze; subsequently killing the teasafe process and re-mounting the image then appears to be impossible. Suggests that there is a problem with how entries are deleted and subsequently cleared after deleting (inc. metadata) all of which appears to secondarily corrupt the image

[benhj]

This bug occurred because the 'next' index of each unlinked block was not being reset to the 'current' index. Have introduced code to do the reset in a FileBlock unlink function which is called from the FileEntry unlink function during file unlinking. This apparent fix has actually broken the test 'TeaSafeTest::testThatDeletingEverythingDeallocatesEverything() blocks in use sizes', I'm not sure why. Needs investigating.