Add option to not install package dependencies

[k4ml]

Consider the following buildout:-

[buildout]
parts = private main

[private]
recipe = mk.recipe.pip
requirements =
    svn+https://example.com/project/trunk

[main]
recipe = zc.recipe.egg
eggs = Django==1.4.2

If somehow project has dependency on Django>=1.4, pip will install Django-1.5 and then zc.recipe.egg will install Django-1.4.2 which waste lot of time.

[k4ml]

This seem to be un-fixable at this moment due to this issue - pypa/pip#1037.

[k4ml]

Another problem related to this is that the dependencies will be installed in site-packages and if the dependencies is not listed in the zc.recipe.egg (since only this package require it), buildout will just add the path to site-packages instead of copying the eggs to eggs directory. This will leave as surprise if for some reason we expect all eggs to be in eggs directory. The only workaround to also listed all the dependencies in zc.recipe.egg eggs option.