The generic bitmap handlers provided by each frontend are called back
from the core and therefore should be in an operation table. This was
one of the very few remaining interfaces stopping the core code from
being split into a library.
This cleans up this header and moves the functionality into more
useful places while reducing the include complexity but only pulling
in whats required.
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
