The move detection code keeps a list of indexes that constituted a move,

which is used to filter out ranges from deleted or replaced lines. This

list was only retained while processing a single chunk, which was fine

in the original version of the move detection code when only inserts and

deletes were considered, but not when taking into account replaced

lines.
This manifested as a problem when working with a moved range of lines

where one or more of the lines were equal to a line previously

considered in a range for a different chunk. Since the previous line

was no longer flagged as being included in a move, it was considered

a valid range for a move, and was then later discarded. This broke up

the actual valid range, causing a gap.
The list is now retained for the entire move detection process, ensuring

that we safely ignore any lines already part of a move.

Unit tests pass.
Tested with a diff exhibiting a gap in a move detection range. The gap

went away.