hung threads are hanging while attempting to lock a destroyed semaphore.

Kill blinker/mouse threads before return.

value of the programs main() function.

returns... this means that the user has closed the program, so we can't
very well wait for the program to exit normally can we?

function to run in the *real* main(), with an exit function which is called
after the programs main() returns (to clean up).

only wake-up interrupt_thread() when *asserting* an interrupt.

PlatformSDK.

with single-thread programs which use SDL audio.

Someone should test tone under Linux with SDL audio...

fields (i.e. to/from/subject)

being build thread-safe.  Other libs (ie: SDL) may define it.

Create new XPDEV_THREAD_SAFE to know that xpdev is suposed to be thread-safe

(Solaris, OSX, Linux) when using SDL as non-static.