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* Reimplementing destroyLocked as death test
* Comments
* Includes to use < > instead of " "
* Don't use c99-isms.

* Documentation
* Exception texts
* Exception safety for a rare situation

The situations are very bad anyway, and that should not happen during
normal operation. So we assert instead.

The previous looked like it should be boolean (there's something good
about lisp's P suffix).

Because of fear of possible future collisions.

* Removed an unneeded friend declaration.
* Typo

- spacing
- new lines for readability
- const
- brace position for catch
- position of ++/--

It should be the same according to the standard, but Clang seems not to
agree with that.

It seems it isn't portable and it's not very useful check.

It can be used to check the thing is locked.

The test may be broken by design. In such case, it should be removed.
But it is left there for now, maybe it's just broken implementation and
someone (the reviewer?) may have an idea how to fix it.

And fix the tests. Some of them were broken a lot, some of them only
little.

To test the Mutexes, we'll need to run threads. So this is mostly to
support some tests for now, but it'll be needed later too.

Created with minimalistic set of functionality. Created a new library
for it, there'll be more thread-related stuff here.