When the fonts distributed with texlive with same family name
as ours are also managed by fontconfig, Qt is not able to
discriminate ours by the style only. In order to be sure Qt
will load our fonts, we change the foundry name from 'PfEd'
to 'LyEd' and augment the font family name with this foundry
name. This only works on *nix, because adding a foundry name
seemingly breaks things on Windows. However, this is a *nix
only problem, seemingly.
This commit adds the mathed command \mathds that selects a
font more appropriate than \mathbb for typesetting the
mathematical symbols for the natural (N), whole numbers (Z),
rational numbers (Q), real numbers (R), complex numbers (C),
and some others.
As in the \mathbb case, only capital letters are supported,
but in addition one can also typeset a symbol often used for
representing the indicator function (\mathds{1}) and the
letters a, h, k.
Fixes bug #11887.
