Allow for building out of tree
Allow for building out of tree

* Gentoo builds all python packages out of tree,
  as is best practice. Using '-Isamtools' implicitly
  assumes that everything is being built inplace.

  See also: https://bugs.gentoo.org/show_bug.cgi?id=629670

kyleabeauchamp/pysam,kyleabeauchamp/pysam,kyleabeauchamp/pysam,kyleabeauchamp/pysam,pysam-developers/pysam,kyleabeauchamp/pysam,pysam-developers/pysam,pysam-developers/pysam,pysam-developers/pysam