DLog-specific tweaks to FastLZ

DLog-specific tweaks to FastLZ

 * add a way to calculate the minimum compression output buffer size
   as required by the interface. This should've probably been baseline.

 * remove the unsafety compiler parameter because I don't want anybody
   to actually tweak it. Removing this safety check is still possible,
   but now somebody has to get his hands dirty and be aware of what
   the exact consequences are, as opposed to just tweaking what is
   essentially an opaque knob.

 * add a comment detailing whence the code was taken.

Change-Id: I1229a9364523b3a5526c9933ccfd09d9292f34a9
Signed-off-by: Michal Bloch <m.bloch@samsung.com>