Added a MADNESS configure flag to disable TBB.
Revert "Added a MADNESS configure flag to disable TBB."

This reverts commit 6c30b7364047d51ce1e1af1e7d8ea7662f4b3a3a.
Added a check to SUMMA that will avoid contracting tile pairs when the result tile is zero.
Removed the redundant world member from ReduceTask.
Added default constructor to ReduceTask and ReducePairTask.
Added a filter to Summa::contract function for zero result tiles with non-zero inputs.
Fixed two bugs in tensor.h function trace, one compiler error and one logic error.
Minor documentation change in tensor.h.
Removed an unused variable from the vesta toolchain file.
Fixed a bug where SparseShape could have a non-zero value for a zero tile as a result of scaling.
Fixed a bug where SparseShape could have a non-zero value for a zero tile as a result of scaling in gemm.
Added Array::truncate() function, which updates the shape of an array object and removes tiles with norms below the zero threshold.
Fix a bug where array data could be deleted too earlier.
- Fixed a spelling error in Array::truncate().
- Array::truncate() will now properly filter tiles that are below the zero threshold.
Fixed typing issues with the new Array::truncate().
Fixed the call to get_pmap() in Array::truncate().
Fixed an ambiguous type in Array::truncate().
Added move constructors and assignment operators to ReduceTask and ReducePairTask.
Updated ReduceTask and ReducePairTask with C++11 style non-copyable semantics.
Updated ReduceTask and ReducePairTask with C++11 style nullptr instead of NULL.