Started p6est project
p6est: added p6est_new(_ext)
p6est: started refine
p6est: vtk compiles

Pretty much a copy, paste, replace from p4est_vtk, but support for nodes
(scale == 1.) is removed, since there is no plan to implement
p6est_nodes.  Possible TODO (use p4est_lnodes instead).
p6est: introduce p2est_quadrant_t, fit into work so far
indent
p6est: simple vtk test passes in serial.
p6est: column and layer refinement compiles.
p6est: refine passing simple test
p6est: wrote most of p6est_coarsen_columns

still need to finish the internal function p6est_coarsen_layer_int
p6est: wrote p6est_coarsen_all_layers

  (prev. p6est_coarsen_layer_int)
p6est: p4est_coarsen_columns passes basic test.
p6est: coarsen_layers passes simple test
p6est: wrote partition
p6est: partition_ext returns shipped
partition: p.user_data is sent as-is, unless data_size > 0.
p6est: partition passes test
p6est: started ghost.h
Merge branch 'merge-ghost-lnodes' into merge-p6est-ghost-lnodes
p6est: ghost passes 2 processor test