makeotfParts: handle relative includes in fea files
makeotfParts: handle relative includes in fea files

bring back a simple version of ufo2fdk's `forceAbsoluteIncludesInFeatures` to convert relative imports into absolute ones before moving files around

moyogo/ufo2ft,googlefonts/ufo2ft,googlei18n/ufo2ft,jamesgk/ufo2ft,jamesgk/ufo2fdk