Metamorph: fix erroneous channel counts

This is what edfc130ef90eb70cb1ad54a9e8450fcd7a84fbec should have done
in the first place.
ChannelMerger isInterleaved() can return true

Added a test to ChannelMerger.isInterleaved() - if canMerge() returned
false, ChannelMerger is effectively "disabled" so the isInterleaved()
call is passed to its delegate Reader.
Add external list of broken URLs to linkcheck_ignore
openThumbBytes interleaves return bytes as needed

When merging channels for a resultant byte[], FormatTools.openThumbBytes
now interleaves the channel arrays if reader.isInterleaved() returns
true.

This should fix interleaved image thumbnails displaying incorrectly.
Merge pull request #397 from hinerm/Interleaved-Fixes-dev44

Interleaved fixes dev_4_4
Merge pull request #387 from melissalinkert/metamorph-channel-count

Metamorph: fix erroneous channel counts
Merge pull request #403 from sbesson/external_broken_links

Add external list of broken URLs to linkcheck_ignore