BatchModes do not take availability of intermediate dates into account

[holtkamp]

Current situation
When using batchMode = 'week' and suppose the week Monday 07-09-2015 to Sunday 13-09-2015, has an intermediate day such as Friday 18-09-2015 which is not available (realised by having the function defined for beforeShowDay return false). I can still click the Monday 07-09-2015, which eventually results in the complete week selected, including the non-available days.

Expected situation
In case an intermediate day of a certain batch is not available, then this batch should also not be allowed to be indicated. So all intermediate dates should be considered as well when determining whether to 'allow' the range selection or not.

[monovertex]

This bug appears with every action that allows you to select multiple days at once. See #468 for another example.