zc.recipe.egg:custom doesn't rebuild on dependency changes

[Dylan Jay]

If you have a custom compiled egg such the one bellow, updating or reinstalling the dependencies (zc.recipe.cmmi) doesn't cause a rebuild of the egg. The result is an egg which fails to run properly at run time if any part of the signature of the dependent cmmi part changes during buildout, for example the version of zc.recipe.cmmi is upgraded.

[Pillow]
recipe = zc.recipe.egg:custom
egg = Pillow
include-dirs =
    ${zlib:location}/include
    ${libjpeg:location}/include
    ${libpng:location}/include
    ${libtiff:location}/include
library-dirs =
    ${zlib:location}/lib
    ${libjpeg:location}/lib
    ${libpng:location}/lib
    ${libtiff:location}/lib
rpath =
    ${zlib:location}/lib
    ${libjpeg:location}/lib
    ${libpng:location}/lib
    ${libtiff:location}/lib

[libjpeg]
recipe = zc.recipe.cmmi
url = http://www.ijg.org/files/jpegsrc.v9.tar.gz

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