FORMUS3IC_LAS3 / embb

- shift initialization of is_active to correct position
- remove unused variable

  (this probably works on MacOS too, but not tested yet)

While on it, fix error message. The missing include file
is not the root cause of the problem. The missing implementation
of embb_core_count_available() is.

HelpScan was implemented wrong -> Scan could be executed be different threads the same time -> FixedSize lists got messed up -> program tried to return wrong pointers to the object pool -> segfault or hang

Moreover, added assertion that checks that only one thread concurrently enters scan, for avoiding these kind of bugs in the future.

Fix internal issue #214, change default doxygen label for api to two (using javascript to collapse to that level)

- Omit doxygen "Makefiles" from tarball (internal issue #221)
- Add executable flag to shell scripts (fixes internal issue #224)