preparations for 0.9 changes

this commit is the first part of a revision of libcppa that removes
the thread-local `self` pointer, `actor_ptr`, and `channel_ptr`
to pave the way for fully type-safe actor programming;
this first step splits the addressing of actors into an `actor`
handle and an `actor_addr`: only the former can be used to send
messages, whereas the latter can only be used to monitor or identify
actors;
next steps will add `typed_actor<>` handles that allow the compiler
to type-check the message passing interface;
the revision is work in progress and this commit does not compile
Further design changes for upcoming 0.9 release
preparations to replace mixin with policy design

this patch makes the first steps for replace the existing mixin-based design
with a more clean and simpler policy-based design for actors
Solve issue #103: Does not build on Linux <2.6.17, issue #108: unused_result warning on g++-4.8.1
Merge pull request #109 from adamcavendish/master

Solve issue #103: Does not build on Linux <2.6.17, issue #108: unused_result warning on g++-4.8.1
documentation & implementations for new policies
fixed selection of poll/epoll impl, closes #110

this patch also gets rid of an unused-private-field-warning
when compiling w/o context switching
Make maximum message size configurable.
Merge pull request #112 from mavam/topic/variable-msg-size

Make the maximum message size configurable.
API refactoring
started to re-implement basic libcppa features
remodeled handling of sync. responses
reimplemented delayed send, fixed logging
fixed uniform type name w/ clang & libstdc++
re-organized policy handling
unified handling of timeout messages
bugfixes (passes test_spawn now)
bugfixes for synchronous messages
added runtime-check to spawn for fiber impl

this patch adds a new static member function to `fiber` that
queries whether libcppa was compiled without fiber support
improved logging & fixed mm bug

this bug fixes a bug where the MM accessed a peer object
after it has been disposed