Compressed section support for libelf prototype.

[Mark Wielaard <mjw at redhat dot com>]

Hi,

The following patch series introduces compressed ELF sections in libelf.
It is a prototype. We want to match the interface that other libelf
implementations will use if possible. This version is slightly different
from the one proposed by the Solaris hackers. I also wrote a different
prototype that was based on the elf_[raw]data/new_data interface (which I
lost that one is a freak fight with git...) That one gave the user a bit
more control mixing compressed/decompressed data. But the current interface
is much simpler. I will post about this on the Generic System V Application
Binary Interface mailinglist where also other proposals have been discussed.
If you have comments on the interface please join the discussion there.
https://groups.google.com/forum/#!forum/generic-abi

Comments on the implementation very welcome here of course.
The main thing that is missing is converting between memory and file
representation before compressing if necessary. Which shouldn't be hard.
There is a XXX comment. Also actually writing the compressed or decompressed
data to the file isn't tested at all. I like to add a new program that lets
you [un]compress sections and/or convert between different compression types
next. That would also be a good testcase for the implementation.

Cheers,

Mark