[subset] Add --ignore-missing-glyphs and --no-ignore-missing-unicodes
[subset] Add --ignore-missing-glyphs and --no-ignore-missing-unicodes

Move glyph checking into the subsetter.  Also fix --gids.  Previous
patch's implementation was wrong as it was picking up glyphs from
sorted glyph-name list, NOT the glyph order!

Fixes https://github.com/behdad/fonttools/issues/34

googlefonts/fonttools,fonttools/fonttools