support parsing of dynamic ELFs w/out section headers

[eliben]

Moving from bitbucket pull request #11 by Mike Frysinger:

support parsing of dynamic ELFs w/out section headers

At runtime, ELFs do not use the section headers at all. Instead, only
the program segments and dynamic tags get used. This means you can
strip the section table completely from an ELF and have it still work.

In practice, people rarely do this, but it's not unheard of. Make the
Dynamic tags work even in these cases by loading the strings table the
same way the runtime loader does:

• parse the symtab address from DT_STRTAB
• locate the file offset via the program segments

In order to avoid circular deps (parsing a dyntag requires walking parsed
dyntags), add a set of internal funcs for returning the raw values.
ave it still work.

[eliben]

Raw patch from the pull request is here: https://dl.dropboxusercontent.com/u/15602400/pyelftools-issue3-patch.patch

[eliben]

Additional information from OP:

$ eu-strip -g --strip-sections a.out
$ readelf -S a.out
<nothing>
$ lddtree.py ./a.out
a.out (interpreter => /lib64/ld-linux-x86-64.so.2)
    libïäöëß.so => None
    libc.so.6 => /lib64/libc.so.6

[vadmium]

I have restored this patch for reference: https://github.com/vadmium/pyelftools/compare/vapier

[vapier]

we should be able to close this now that my updated change has been merged