This should ensure, that the event is definitely cleared.

These functions should be thread safe.

Switch off polling-based (addChore) processing of threads

Add event-based interruption of GVL-released functions.

This allows to safely execute GUI code from other threads.

This works for sockets only for now.

This is the only function that is currently required to acquire the GVL.
Other FXRbCall functions could be wrapped equally.

This is just enough for loadPixel/savePixel, but if other methods
release the GVL, potentially all other callback functions could
be called. These are now yet wrapped by gvl-aware wrappers.

This also fixes some build system checks, that should be for the target system.

without check.

This solves crashes of kind:
	[BUG] rb_gc_mark(): 0x00000003f54af8 is T_ZOMBIE

All parameters to Ruby event blocks or overloaded methods are converted to
proper Ruby classes or wrapped by appropriate wrapper classes for borrowed
objects. The wrapper classes are registered, to keep the connection between
C-pointer (the borrowed object) and the wrapping Ruby object. This connection
is canceled either when the borrowed object is destroyed or the Ruby wrapper
is free'd. If neither of them happens, the wrapper object is re-used for the
next call.

This worked good with Ruby-1.8, which has one big mark and sweep run.
Ruby-2.2 introduced incremental GC and has several mark and sweep runs, so
that marks and sweeps are quite independent. Therefor we re-used objects,
that are already maked for sweeping (so called T_ZOMBIE).

This patch releases the connection between borrowed object and it's wrapper
object after each call into Ruby code. Therefore the wrapper object isn't
re-used, but a new one is created for each param to each call. The wrapper
objects are later free'd by the GC. This patch could have a negative
performance impact.

Static linking all dependent libraries into each ruby version (from
1.8 to 2.2) would blow up the gem to >20MB.