Remove the use of reachability fences

We don't need them because the use of the native pointer is contained within the critical section of the pin, as represented by the StampedLock. This locking similarly constrains the life-time of the page objects.
In essence, use of the native pointer cannot move above taking the lock, nor bellow its release, and since the MuninnPage objects are themselves StampedLocks, their life-times is guaranteed to extend at least as far as their last lock release.
Remove use of exceptions for control flow in Node and Relationship scan operations
Merge pull request #3628 from chrisvest/2.2-except-ctrl-flow

Don't rely on exceptions for control flow
Fixed typo in documentation.

Theere -> There.
Merge remote-tracking branch 'upstream/2.1-maint'
Remove a file accidentally committed in June
Merge branch '2.1-maint'
Merge pull request #3629 from chrisvest/2.2-reachability

Remove the use of reachability fences
Fixes leak of file mapping from count store on error during file open

It is possible for the count store files to be perceived as
 unusable in case the header information or some key data is not
 consistent. While not a fatal error, this is communicated by
 throwing an IOException which is caught and the paged portion
 of the opened file will be unmapped. However, before this
 fix it was that IOException would be ignored by the responsible
 catch clause, leading to the leak of the file map and the
 inability of the database to shutdown since that file was
 mapped.
This patch fixes the issue by catching all possible Exceptions
 thrown during open and not only RuntimeExceptions as before.
Merge pull request #3635 from digitalstain/2.2-countstore-exception

Fixes leak of file mapping from count store on error during file open