Fix-up post-processing to handle name-space packages

If preserve_egg_dir is False, and conda build were building a name-space package this would cause a problem as the directory already existed. 

This patch adds a utility:  copy_into  and checks to see if the destination directory exists and if so, copies the files from the egg directory into the destination directory.   

Tested with zope.event, zope.interface, and zope.component