versions aren't fetched intelligent
buildout seems to fetch dependencies when running buildout without intelligence. Example:
buildout config containing eggs package.x, package.y
package.x requires package.z <0.2
package.y requires package.z
buildout now may fetch the latest version of package.z ( e.g. 0.3) when proceding package.y
proceding package.x will lead to a version conflict.
buildout should download <0.2 as package.y doesn't state a version number