msp430: provide oneway-malloc implicitly

For MSP430 boards oneway-malloc is already used *if* `malloc.h` was
included. The problem is that `malloc.h` is not a standard header, even
though it is common. `stdlib.h` in the right place to look for
`malloc()` and friends.

This change removes this discrepancy. `malloc()` is just named like
that, without the leading underscore. The symbols now are weak, which
means that they won't override library functions if MSP's standard
library will provide these functions at some point. (Unlikely, since
using `malloc()` on tiny systems is less then optimal ...)

Closes #1061 and #863.
Add doxygen comments to MSP's oneway malloc
msp/tests: remove blacklist from test_bloom_bytes

Issue #1061 was fixed.
Merge pull request #1182 from Kijewski/msp-oneway-malloc

msp430: provide oneway-malloc implicitly