[BLFS] Ticket #1730: clean the dependency list
With the new xsl/dependencies.xsl, the full dependency list is generated.
We compare the version and installed version gotten from packages.xml
using xsl/get_version.xsl and only install if the installed version is
lower than the available version. Since the installed version returned
by get_version.xsl for a non installed package is 0, that version is
always lower than the available version and the package is installed.
Note that if a package does not exist, both versions are empty, and
they compare as equal with our method. So they are never installed...
