0.10.1 — field-report fixes and real strength levels

GNU Backgammon for Android 0.10.1

A follow-up to 0.10.0 with the fixes from the first field reports. Everything in
0.10.0 that had not yet reached a device is folded in here.

Added

• Three stronger playing levels — Expert (0-ply, no noise), World class
  (2-ply), Grandmaster (3-ply) — exposing gnubg's real strength. The four
  original levels are 0-ply with noise; the strongest of those still let an
  occasional weak move through.

Fixed

• Saved SGF names were swapped: the human was written as "gnubg", the engine
  as "user". The port's player 0 is the human; the names now match.
• The strongest level was not strong. "Advanced" is a 0-ply-with-noise preset
  and occasionally played a poor move (a 24/16 on an opening 53 was reported).
  Underneath, the per-player move filter was never initialised, which silently
  broke multi-ply evaluation; fixing it is what makes the new levels correct.
• Start Match could vanish on short landscape phones, squeezed to zero height
  by a weighted layout. It is now pinned.
• The Analyse screen could hide its own output — the ranked plays, the
  editor's Analyse button, and long labels fell off short panes. Regions are now
  pinned or bounded; labels never wrap.
• A fresh clone could not build: engine headers the Android build compiles
  (sound.h, export.h, movefilters.inc, boarddim.h, progress.h,
  openurl.h) were hidden by .gitignore. All tracked now, with
  tools/check_buildable_clone.sh as a guard.
• The release build is signed, so its APK installs.