Further clarity and speed cleanups of minibidi:

Further clarity and speed cleanups of minibidi:
 - rewrote the reversal loop in flipThisRun to be considerably clearer
 - rewrote leastGreaterOdd and leastGreaterEven as bit-twiddling macros
 - replaced malloc/free with snewn/sfree
 - lost some gratuitous repeat calls of getType on the same character
And most noticeably:
 - got rid of minibidi.h, since it was entirely full of minibidi.c
   internals (including constant data definitions!) and wasn't used
   to provide an external interface at all. Everything in it has
   been folded into minibidi.c.

git-svn-id: svn://svn.tartarus.org/sgt/putty@4963 cda61777-01e9-0310-a592-d414129be87e