sf panics scanning fmt/1172 file of skeleton suite with freedesktop.org identifier

[richardlehane]

discovered by @ross-spencer
to reproduce: 1) use deluxe.sig or freedesktop.sig; 2) scan fmt-1172 file within skeleton suite
Panics at line 456 of mimeinfo/identifier.go applyscore method.

[richardlehane]

maybe due to the fact that freedesktop.org has a double-entry for font/woff

[richardlehane]

I've tested a fix on the develop branch that reports an error where a mimeinfo signature file duplicates IDs. In doing so, discovered both the freedesktop.org.xml and tika-mimetypes.xml files have duplicate IDs.
In both cases, these appear to be errors in those files:

• in the freedesktop case, the second entry for font/woff should be font/woff2
• in tika's case, the whole entry for application/x-gtar is duplicated for some reason.