This commit makes several changes to Protect and related moves in both
Gen 4 and Gen 5:

1) In Gen 4, the chance of protecting succeeding does not fall below
   1/8, which has now been corrected in this commit. Previously, the
   chance of success in Gen 4 was allowed to drop all the way to
   1/(2**32) as in Gen 5.

   Please see upokecenter for the correct mechanics:
     http://upokecenter.dreamhosters.com/dex/?lang=en&move=182

   For Protect and friends, Smogon currently says that the chance of
   success does not fall below 50%, which is inconsistent both with the
   current Pokemon Showdown! behaviour and with upokecenter. It is
   pretty much certain that upokecenter is accurate here, since it is
   based directly on the in-game data. This commit implements the
   upokecenter mechanics.

2) This commit also consolidates some duplicate code with Protect and
   friends by moving the miss chance logic to an event of the 'stall'
   volatile called onStallMove. This allows me to remove some duplicate
   code from moves.js.

3) Currently, some but not all of Protect and friends have a flag
   called stallingMove set to true. This flag does not appear to be used
   for anything. However, for consistency, I have set it to true for all
   the "stall moves", as opposed to just a subset of them.
Use this.effect for constant effect property.