Debundle libsc from p4est package; introduce a new package libsc

This reflects current upstream development in debundling libsc from p4est.
Bump p4est to version 0.3.5

  * Debundle libsc from p4est
  * Fix build system so that autoreconf works without bundled sc
  * fix sonaming
Merge pull request #199 from tamiko/bump_p4est

Bump p4est; new ebuild for libsc