Untested but working first attempt to nibble rows below first lower boundary and above last upper boundary.

t/pt-table-checksum/basics.t

@@ -20,6 +20,10 @@ $ENV{PERCONA_TOOLKIT_TEST_USE_DSN_NAMES} = 1;
 use Data::Dumper;
 use PerconaTest;
 use Sandbox;
+
+# Fix @INC because pt-table-checksum uses subclass OobNibbleIterator.
+shift @INC;  # our unshift (above)
+shift @INC;  # PerconaTest's unshift
 require "$trunk/bin/pt-table-checksum";
 
 my $dp = new DSNParser(opts=>$dsn_opts);