Show C++11 extension warnings by default with Clang
In Clang, disable `override` in C++03 mode
Disable -Werror in try_compile

As compilers become more advanced in their static analysis, we might
inadvertently disable some C++11 features because a new compiler version
finds something unrelated to complain about in our minimal examples in
the cpp0xtest folder.

We would rather fix warnings manually than automatically ensure that
C++11 features never emit any warnings.
Merge branch 'issue_145' to fix #145
doc/pipelining.dox: Fix reference to old API
Add support for unit tests with 5 arguments
Support tests with 6 arguments.
Rename position.h -> stream_position.h
Make stream_position::offset public
stream_position: Ensure that operator< is a total order
stream_position: Add constructors for pointers to beginning/end
file_stream::set_position: Handle stream_position::end
Rewrite stream_position documentation
Merge branch 'stream_position'

Closes #149.
Remove remnants of the pipe_segment name
Add pipelining nodes vfork and fork_to_virtual.

vfork is basically fork but with virtual nodes instead of ordinary
pipelining nodes.
Add ut-pipelining virtual_fork
Dont complain about subindicators when an exception is in flight
B-tree work in progress.
B-tree work in progress.