Cover the previously-unexercised code paths flagged by Coveralls:
- writer: month and year date grouping, and a fractional numeric interval
(the non-integer num() path);
- reader: reading an explicit dataField subtotal attribute back from a saved
file;
- worksheet: the getPivotTables() alias, addPivotTable(), case-insensitive
getPivotTableByName(), the no-match lookup, and removePivotTableCollection().
Cover the PivotFieldGroup, PivotField, PivotCacheDefinition and PivotTable
accessors that were not exercised by the reader/builder tests (numeric and
date grouping getters, field-group storage on the cache definition, pivot
field setters, and PivotTable::__toString), restoring code coverage.
saifulislamferoz