Changed includes to /usr
unsquashfs: add support for LZMA magics

Some vendor (e.g. Thomson/Technicolor) use a different super block magic
to indicate LZMA compression:

  qshs (0x71736873) - LZMA compression
  shsq (0x73687371) - LZMA compression, SWAPPED fields

Add support for detecting this and enable extraction for filesystems
from those firmwares.

Signed-off-by: Jonas Gorski <jonas.gorski@gmail.com>
Tested-by: Antonio Ospite <ospite@studenti.unina.it>