This required a fix to fontTools/cffLib. When reading a CFF2 variable font (VF) from XML, the VF state in FontDict and PrivateDict does not get set. I made a temporary fix by adding a loop to set PrivateDict.vstore for all the PrivateDict objects after the XML file has been read. This should not be necessary, and in the near future I will revisit both this issue, and the related use of isCFF2 when compiling/decompiling.
Add test for building CFF2 variable font with a call to varLib.build().
The 'dollar' glyph in the test font is deliberately slightly malformed, with flat curves, in order to exercise the code for dealing with some of the differences in masters designs that can arise from T2 charstring optimization.
