Fix TODOs from 2.4.7

[s-martin]

Check the old TODOs, if still applicable and fix them:

• make the library thread-safe
• xml input and output for saving the state of genomes and evolutions
• use double rather than float
• allow run-time modification of the random number generator
• get rid of all the casts (e.g. GASelector.C) for signed/unsigned
• be consistent in use of signed/unsigned in the class apis
• use bits for the bit-based genomes so that we reduce memory use by a factor of 8
• enable concurrent builds on the same source tree
• make galib 64-bit clean (remove the dangerous casts)

taken from https://github.com/s-martin/galib/blob/ee43915cdbe26e153c1cece2fc7b2638e43ba161/TODO.md