[Rock-dev] Issue with fipa_acl (and temporary workaround)

[Sylvain Joyeux]

I found out (the hard way) that three of fipa_acl's files take (each)
more than 2.6G of memory to compile (I stopped at 2.6 because my
laptop only has 3). This can bring down a lot of machines.

Until we find a proper solution, I've removed fipa_acl from the
default, which means that it can be built if explicitly selected (in
layout or depended-upon), but won't build if only using the 'rock'
package set in the layout.

Sylvain