QFont does not consider font family substitution table when handed a list of family names

When QFont is handed a comma-separated list of font family names, it successfully uses the first font from the list it can find.

An example: On a system with both "Linux Libertine" and "Tahoma" installed, this will succeed in using "Linux Libertine":

QFont("Linux Libertine,Tahoma");

It also succeeds with leading family names that are not installed in the system, i.e. this will still succeed in using "Linux Libertine":

QFont("Fakefamily,Linux Libertine,Tahoma");

Now, QFont also offers the ability to add substitutions. This will set up a substitution of "Fakefamily" with "Linux Libertine":

QFont::insertSubstitution("Fakefamily", "Linux Libertine");

Afterwards, this will succeed in using "Linux Libertine":

QFont("Fakefamily");

Now the bug. Despite the substitution, this will NOT succeed in using Linux Libertine:

QFont("Fakefamily,Tahoma");

This is a problem in the real word. CSS 3's @font-face rule allows specifying custom names for underlying document-supplied font files. KDE's KHTML browser engine adds such font files using QFontDatabase::addApplicationFont(), and then sets up substitutions for the document-specified custom names. However, if a CSS rule refers not only to that custom name but includes a list of several families, the comma-separated string KHTML builds and hands to QFont will not work, as explained above.