ACCUMULO-1628 Fixes issue after previous changes which interrupted a deep-copy

Pushes the interrupt flag from the SourceSwitchingIterator down to the
FileManager and InMemoryMap. This should avoid passing the interrupt
into a deep copy which isn't supported. Adds some more tests which
previously caused the edge case which is now fixed.

Signed-off-by: Josh Elser <elserj@apache.org>
Merge branch '1.5.2-SNAPSHOT' into 1.6.1-SNAPSHOT

Conflicts:
	server/tserver/src/main/java/org/apache/accumulo/tserver/Tablet.java
	server/tserver/src/test/java/org/apache/accumulo/tserver/InMemoryMapTest.java