JPSSnagg

Fixed JPSS-86 and JPSS-87.  Region references are now created for hyperslabs with no stored data because they contain entirely fill values.  nagg will now handle files that have missing region references and create the missing references in the output files.  
While addressing these issues, a file was created with a 12 granule aggregation but only one granule dataset in the /Data_Products group.  The file was not corrupted, but nagg failed when it could not find expected granule datasets.  The error message was improved to indicate the problem.

Tests and test files added for datasets with all fill values, for files with missing region references, and for files that can be opened but are missing granule datsets.

Tested on jam and platypus with gcc & icc and extensive data tests.