First of all, many thanks for reenabling the standard ligatures (ff fi fl ffi
ffl) in Sans!  The ligatures ffi and ffl are still broken, however, because you
only specify the substitutions:

   f + f + i -> ffi   /   f + f + l -> ffl

As a consequence, when rendering the character sequences ffi or ffl, Pango first
combines the two f into one ff ligature, and when it gets to the i or l part,
the substitution rule no longer applies because there are no longer two f plus i
/ l in the input, but one ff ligature plus i / l.  I believe the right thing to
do (and it definitely works) is to have two substitution, one of which takes the
precombined ff ligature as input:

   f + f + i -> ffi   /   f + f + l -> ffl
   ff    + i -> ffi   /   ff    + l -> ffl

Also, it would be really nice if the standard ligatures could also be reenabled
in all other DejaVu fonts (except for SansMono, of course).

Thanks,
Stefan