Fixed bug: too many Ns added by spliced_seq

If sequence of an exon is not found, Spliced_seq should add the number
of Ns corresponding to just that exon.
Add tests for spliced_seq remote sequence handling

Add tests to check that the length of spliced_seq is the same when it
resorts to padding with Ns after failing to locate the remote source
sequence for some exons. Also checks that spliced_seq throws the
appropriate warning. The test throws a warning itself if it cannot
complete the tests e.g. due to lack of Genbank access.
Splicedseq.t: Reorganized new tests to use "-requires_networking"
for online tests, and made a format cleaning
Localize Storable options instead of enabling them globally

Otherwise any external code relying on the Storable defaults will be
rudely (and unsafely!) surprised if a Bio::DB::SeqFeature::Store object
is created in the same process.

I'm not sure if $forgive_me = 1 is strictly necessary, but I'm leaving
it.  It can't hurt too much and may paper over other refs which
Data::Dumper can serialize/inflate but Storable can't.
Let Data::Dumper deparse CODE refs to serialize them, just like Storable

Otherwise they are replaced by sub { "DUMMY" }.
Add tsibley's work to Changes file
Clean up and move to proper spot
(Thomas Sibley): Tell Storable to freeze and thaw CODE refs

By default it won't for security.

This reverts commit 5dd8e967998c8ccc3305c5c41c4c2d6f4b6a3395: "skip
tests if the cloning class used happens to be Storable, see bug #3447".

The failing tests from Redmine issue #3447, t/Seq/Seq.t and
t/SeqTools/SeqUtils.t, pass for me both with and without Clone
available.  I tested using -MDevel::Hide=-from:children,Clone.