Implement garbage collection using libgc

[plajjan]

Proposal

Use libgc for garbage collection!

Motivation

Acton needs a GC!

Alternatives

Naturally the long term solution is a custom GC for Acton that interoperates well with other parts of Acton providing the best solution for performance etc. In the meantime, any GC is better than no GC.

[plajjan]

@aagapi I'd like your input on one topic. The DB client needs to malloc things with GC, just like the rest of RTS. It doesn't matter if it's libgc, which I'm trying to implement here, or if it is the longer term custom-written GC for Acton, we still need to use a GC_MALLOC.

I haven't looked in detail at how DB client mallocs stuff but I presume it mallocs, like when we get respone data from DB we have to malloc that up right.

There are shared files between the DB client and actondb. I assume that you want manual memory management in actondb. I think this means we need to compile these support files twice, once for actondb with standard malloc and once for DB client with GC_MALLOC. I can set up the Makefile stuff for that but I do have to inject which malloc to use, so my suggestion is to replace all mallocs, callos, reallocs & free with like ACT_MALLOC, ACT_CALLOC etc, and then I can define this as a macro depending on how I am compiling it.

What do you think? would this be an acceptable approach or do you see a better alternative?

[plajjan]

Fixed by #964. Closing.