Fix CFF flavored font embedding for multiple output

Fix CFF flavored font embedding for multiple output

For multiple output (e.g. `-dbackend=eps`),
conflict checking needs to be done within each output.

Otherwise, the font which is embedded in the prior output
is not embedded in the subsequent output.

[lemzwerg, 2016-07-04 21:31:17]

LGTM

[trueroad, 2016-07-11 13:59:34]

I've pushed to staging.

Issue 4918: Fix CFF flavored font embedding for multiple output
commit 4164bfb62950c46517a21ad1d80131ce27868aa1