Fix merge_sorter segfault on some merge tree heights
Add ut-merge_sort tall_tree test
Add missing item_type to vfork_node
Add pretty_print class.
Use pretty print class in memory-limit-exceeded warning. Fixes #156.
Comment out debug output in compressor_thread::impl::process_write_request. Fixes #157.
pipelining/runtime: Make get_item_sources/sinks take dependency edges into account
Add pipeline::then to insert ordering between otherwise unordered pipelines

Fixes #158.
Remove remnant of the pipe_segment in the pipelining implementation
file_stream::read/write and others: Throw exception when stream is not open
Add missing include
Make pipelining buffer use compressed streams. Fixes #161.
Add pull_tee.
Fix file_accessor::posix throwing an exception when writing large files.
CMakeLists.txt: Disable override unless CXX_FLAGS includes -std=c++0x
Implement datastructure support in the pipelining framework.
Add datastructure section to documentation.
Update pipelining method matrix in the documentation.
Add pipelining datastructures unit tests.
Fix pipelining datastructures get_datastructure and set_datastructure methods.