[M3commit] [modula3/cm3] c15e8b: Fix Rd bug reported by Mika.

[GitHub]

  Branch: refs/heads/master
  Home:   https://github.com/modula3/cm3
  Commit: c15e8bf9a4958fe1f22e50f95ead1fef61a007bc
      https://github.com/modula3/cm3/commit/c15e8bf9a4958fe1f22e50f95ead1fef61a007bc
  Author: Rodney Bates <rodney.m.bates at acm.org>
  Date:   2017-12-14 (Thu, 14 Dec 2017)

  Changed paths:
    M m3-libs/libm3/src/rw/Rd.m3

  Log Message:
  -----------
  Fix Rd bug reported by Mika.

In which CharsReady incorrectly was blocking.

Also fix a bug in GetSub, in cases where a lot of ungetting and
regetting happens.

Also fix some places where closed check was not happening as
aggressively as in the specifications in the comments in Rd.i3.