Calculate all cache sizes from single memory cache size option and sanity check
have a single global struct to hold all parameters instead of several individual variables
svn path=/trunk/netsurf/; revision=12784
Current periodic cache clean algorithm is poor and requires replacing with something suitable (probably a segregated LRU)
The speculative load algorithm is likewise poor and only uses the image size to make a decision.
svn path=/trunk/netsurf/; revision=12720