If an unevenly sized allocation is requested, the next buffer handed
out would start at an unaligned address.
Fix this by rounding up to the next word-sized allocation size.
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.
