Allow an MTD partition so serve as a source "file" in applypatch,
using a magically-formatted 'filename' that specifies the partition
name, size of data to read, and expected hash. Build incremental OTAs
that update the recovery image via a patch.
Images (like boot and recovery) consist of large sections of gzipped
data interspersed with other data. To do effective binary patching of
these files, we need to apply patches to the gzipped parts in
'uncompressed space', that is, we decompress, apply a patch, then
recompress to obtain the desired output.
This change defines a new format with these patches, which is
basically a description of how the source and target files are to be
divided up into chunks and a bsdiff patch for each chunk. We add a
new host executable, "imgdiff", for generating these patches from
source and target images, and add support in applypatch for
recognizing this format and applying it on the device.
Allow applypatch to use different filenames for the source and target.
(Using the same filename is still fine; in fact the target filename
can be specified as "-" to mean "same as the source file.) This will
allow us to still use diffs in the case of files being renamed, and
will allow us to use diffs for the boot and recovery images.
