mdsim/particle: make space dimension mandatory

Conflicting space dimensions between box and particle are a common error
in two-dimensional simulation scripts (with a cumbersome error message
on failed overload resolution). The missing argument "dimension" to
particle() is not noticed in 3D simulations. Thus, we make it mandatory
in any dimension.
packages.mk: add GDB, the GNU project debugger

The installed version on OpenSuSE 13.1 is buggy and crashes when running
on the HALMD binary.