Recovery strategy testing

Test added for the "retain" recovery strategy.  This strategy makes sure
a full history of index changes is made so that if the Ledger is wiped
out, the Ledger cna be fully rebuilt from the Journal.

This exposed two journal compaction problems

- The BestRun selected did not have the source files correctly sorted in
order before compaction
-  The compaction process incorrectly dealt with the KeyDelta object
left after a compaction - i.e. compacting twice the same key caused that
key history to be lost.

These issues have now been corrected.

test/end_to_end/basic_SUITE.erl

@@ -8,7 +8,7 @@
             fetchput_snapshot/1,
             load_and_count/1,
             load_and_count_withdelete/1,
-            space_clear_ondelete_test/1
+            space_clear_ondelete/1
             ]).
 
 all() -> [
@@ -18,7 +18,7 @@ all() -> [
             fetchput_snapshot,
             load_and_count ,
             load_and_count_withdelete,
-            space_clear_ondelete_test
+            space_clear_ondelete
             ].
 
 
@@ -398,8 +398,7 @@ load_and_count_withdelete(_Config) ->
     testutil:reset_filestructure().
 
 
-space_clear_ondelete_test(_Config) ->
-    % Test is a work in progress
+space_clear_ondelete(_Config) ->
     RootPath = testutil:reset_filestructure(),
     StartOpts1 = #bookie_options{root_path=RootPath, max_journalsize=20000000},
     {ok, Book1} = leveled_bookie:book_start(StartOpts1),