use internal lzmaextract for xz and 7z as an alternative

Make sure binwalk always opens files with utf-8 encoding

In Python 3.4, if the interpreter is launched with e.g. LANG=C environment,
binwalk fails with UnicodeDecodeError, since it tries to decode included
magic files (such as src/binwalk/magic/linux) with ascii codec. This patch
makes sure that utf-8 codec is always used.

Add signature for Android bootimg

update crypto signatures for elliptic curve keys

Fix minor spelling error in warning message.

ubifs extraction