This code should be cleaner and easier to understand. It also provides
the ability to spread image decompression on all CPU core. I currently
set it to the exact number of CPU core you have in your machine, if you
find case where it slow down your EFL apps too much, we can reduce this
to give at least one core to evas.
All previous bugs related with async preload are gone, hopefully no
new one are in. Please report any problem with backtrace to me.
SVN revision: 44537
b0ffd95878