Started to add executors
More work on executors, refactoring parts of the thread manager
Fixing set_thread_state for thread_pool_executor
Unifying executor semantics
Cosmetics
Merge branch 'master' into executors
Add check whether finalize was already called.
More refinement for executors. Executed tasks keep executor alive. Added initial state and run_now argument to add and try_add.
Added overloads for async, apply, future::then, packaged_task, and futures_factory taking an executor
Fixing const correctness problem
Merge branch 'master' into executors

Conflicts:
	src/hpx_init.cpp
Fixed accumulator example
Adding minimal resource_manager to executors
Merge branch 'master' into executors
Merge branch 'master' into executors
Fix #667: Not reading ini file properly
Some minor documentation work
Working on resource allocation for executors
Merge branch 'master' into executors
Tweaking external build system