This commit implements working Entropy package delta download for
both single fetch and multifetch feature. It is fault tolerant and
the usual behaviour will be triggered as fallback.
Due to the memory requirements of bspatch, edelta won't be used for
files bigger than 10Mb (this is hardcoded inside entropy-pkgdelta-generator).
.edelta files are automatically generated by entropy-pkgdelta-generator,
inside a cron job on our servers. This feature is completely optional,
but can be easily implemented by 3rd parties by simply using the
generator app above, everything will be handled automatically (bsdiff
required).
Fabio Erculiani
71a7e59f64