app-text/sigil: version bump and general maintenance

app-text/sigil: version bump and general maintenance

- pruned old versions: 0.8.5, 0.8.6, 0.8.6-r1, 0.8.900_pre
- version bump: added 0.8.901_pre
  This bump introduces the use of python-single-r1.eclass as well as
  several python dependencies needed for sigil's plugins.
- fixed bug #561690: added >=sys-devel/gcc-4.8 to DEPEND for
  0.8.7-r1 (revbump) and 0.8.901_pre
- fixed bug #562142: This was introduced by my fix for bug #440704.
  Changing the fix to simply remove 'CMAKE_BUILD_TYPE="Release"' and NOT
  rely on semi-random sed-operations. (thx to mgorny for suggesting the
  fix)
- removed eutils.eclass from 0.8.7-r1 (revbump) and 0.8.901_pre (thx to
  kensington for pointing it out)

(cherry picked from commit 543bd475cd622887f5bad8a7b7ea60205433128c)