Fontmake uses inconsistent naming on single glyph files

I was running fontmake on single glyph slices of a source file (for building fonts with brace layers) as well as the full source file and encountered the odd scenario where the naming conventions did not line up between the main font file and the sliced font files (i.e. the full file had the glyph named /g but the sliced file had uni0067). This does not seem to be an issue for suffixed glyph names such as /s.sc

I do not believe I have modified anything when slicing the source file that would cause this, especially since suffixed glyphs behave as expected. The sliced source files themselves correspond to the names in the original source.

For reference here are the sliced sources, corresponding ttfs, and the full ttf:
[Hepta-sources.zip](https://github.com/googlei18n/fontmake/files/2659368/Hepta-sources.zip)