added NORETURNs to functions that should not return
and added `UNREACHABLE();` to hint the compiler unreachable lines

added right signature for first parameter of `thread_stack_init()`
added `UNREACHABLE();` macro to `cpu/lpc1768/atom.c` and `cpu/msp430-common/cpu.c`
Exclude *.c files from make doc
Add process indicator to compile_test.py
unittests: separate test suites from main.c

This change removes the need to patch the main.c if you add or remove a
test suite. A test suite in `tests/unittests/tests-XXX` needs to export
the function `void tests_XXX(void)`, which gets called by `main()`.

The `tests-XXX/Makefile` looks like your average module:
```
MODULE = tests-XXX
include $(RIOTBASE)/Makefile.base
```
native: fixup #1145: function declaration
Merge pull request #1172 from Kijewski/fixup-166b88f1

native: fixup #1145: function declaration
Merge pull request #1168 from Kijewski/unittests-use-subfolders-and-dark-magic

unittests: separate test suites from main.c
Introduce macro to define files that should be deleted on make clean
Move .elf file to it's own target
Make directory creation in object compilation more makey
make: put buildtest goals into an own file

`Makefile.include` is too long as is.
make: delete everything in buildtest beforehand
make: supply `-j` on `buildtest`

We support `make -j` for a while now. `make buildtest` takes ages to
finish. So just supply `-j` on buildtest.
Merge pull request #1169 from Kijewski/buildtest-minus-j

make: supply `-j` on `buildtest`
shell: renaming `isnumber` to `is_number` in sc_net_if.c

fix name collision on OS X by renaming
net: handle macro redefinitions for OS X

undefine macros and reorder header includes to get rid of system
defined macros on OS X

fixes #1165
msp430: fix missing members in `struct tm`

Closes #1150.
make: Remove `Makefile.unsupported`

This mechanism was replaced by #535. It was only used in one project.
Merge pull request #1137 from authmillenon/no_c_doc

doc: Exclude *.c files from make doc
Merge pull request #1098 from authmillenon/make-addon

make: Make make more flexible