* Add "fd_pipes" and "returnpid" parameters to doebuild() and pass

 * Add "fd_pipes" and "returnpid" parameters to doebuild() and pass
   these into spawn calls, enabling ebuild processes to execute
   asynchronously.

 * Add a EbuildPhase class that's derived from the pty logging code
   inside portage.spawn().

 * Integrate post-phase code from spawnebuild() into EbuildBuild.execute()
   so that it still gets called even though doebuild() calls execute
   asynchronously.

svn path=/main/trunk/; revision=10849