support boost context 1.51
remove fiber::m_size, not needed
add valgrind stack tracking
add cmake check for valgrind.h
fix build when no boost_context available
fix compile error when using boost 1.52
add configure option to disable qt examples only
maintenance & type_list interface changes

the type_list interface changed and the class itself no longer has
any members, tl_size<>, tl_head<>, etc. must be used instead;
these "template functions" also work with any variadic template class;
this patch also changes some code parts to be more consistent with
libcppa's coding style and naming convention
new class: int_list

this class provides a convenient way to access int parameter packs
in the same way as type_list does for type parameter packs
don't use std::begin/std::end in memory interface

the use of std::begin/std::end has reported to cause ambiguity errors
on some compilers
cleaned up code in producer_consumer_list
better debug output and new requirement
optimized loop and added requirements
Merge branch 'master' into unstable
Merge branch 'master' of https://github.com/toffaletti/libcppa into unstable
reduced #ifdef statements to minimum
solved bug in chaining impl, fixes #83
complement documentation of intrusive ptr
fixed chaining for exited context-switching actors
more output in test__spawn
provide `aout` "stream" and use it in examples

the `aout` stream acts like `cout`, but instead of printing content
directly to the terminal, `aout` sends all strings to an actor
that has a per-sender map to prevent interleaved output
fix minor build issues