Merge pull request #65 from gawrysz/SFC_neighbors

Sfc neighbors (PRACE 2010PA1757)
[si] Port changes from si_tweaks to master
[compilers/default] -funroll-loops do more harm than good
Merge pull request #66 from Xarthisius/si_update

[streaming_global] update
Merge pull request #67 from gawrysz/SFC_neighbors

Sfc neighbors
[cg_list_neighbors] comments
[sort_segment_list] another sortable type, this time for merging of MPI messages
[sort_cg_list] doxy
[merge_segments] added stub type for merging segments
[sortable_list] remove non-essential methods from the abstract type
collected info on segments to communicate on current level
[sort_segment_list] provided safe [lu]_bound values for non-allocates lists
sorted the lists of segments
computed offsets within the lists of segments
added pointer to source/target grid container to the list of segments
[merge_segments] do not use merged MPI on local boundaries when there is a local communication without pointer to right grid container set.
[cg_list_neighbors] comment
remember also the direction of segments to be merged for MPI
[cg_list_bnd] internal_boundaries split into local and MPI exchanges
[cg_list_bnd] moved some duplicated code to a better place