Bug fix in mpi_tree.txx
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mpi_tree.txx: bug fix in tree construction

bug fix in  MPI_Tree::Initialize(...) for very small number of initial points.
Bug fix in MPI_Node<T>::Unpack(...)
Replaced upward-pass functions with optimized versions.
allow MultipoleOrder()==0
minor changes
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bug fixes, everything works!
Add memory manager.
Changes for Intel Phi native build.
bug fixes, optimizations
Optimize 2:1 balance algorithm.
update scripts.
clean up
Merge branch 'feature/mpi-sparse' into develop
update scripts (Helmholtz).
load balancing, bug fixes.
update example fmm_cheb.cpp
Optimize singular integration: cheb_integ(...)