[autohint] Fix temp files solution

[miguelsousa]

Fixes #244

[cjchapman]

• need to add import of TTLibError from fontTools, as it is used in openOpenTypeFile() -- line 969
• fontFileName is undefined in openOpenTypeFile() -- line 975
• kProcessedGlyphsLayer is not used and should not be imported
• sys, os, re, time, tempfile, and warnings are not used and should not be imported

[miguelsousa]

@cjchapman autohint is due to be replaced with psautohint. I don't think the fixes and clean ups you listed are worth doing.

[cjchapman]

@miguelsousa OK. For the record, I'm approving this PR on the basis that the issues I'm concerned about are not in the areas changed by the PR. :-)

[miguelsousa]

@cjchapman don't worry, these shaddy approvals shall not taint your reputation 😜

[cjchapman]

@miguelsousa It's the whole public record thing that worries me, e.g. what if my daughter reads this someday and says, "Seriously Dad, you approved this?!" 😉