fallback to the another method to lock when link() failed

Bug 82358 - FcAtomicLock fails on OS X on network mounts
https://bugs.freedesktop.org/show_bug.cgi?id=82358
Increase the refcount in FcConfigSetCurrent()

https://bugs.freedesktop.org/show_bug.cgi?id=82432
Fix the memory leak in fc-cat
Note FcConfigSetCurrent() increases the refcount in document
Revert "[fcmatch] When matching, reserve score 0 for when elements don't exist"

This reverts commit a5a384c5ffb479e095092c2aaedd406f8785280a.

I don't remember what I had in mind for "We will use this property later.", but
the change was wrong.  If a font pattern doesn't have any value for element,
it must be interpretted as "it matches any value perfectly.  And "perfectly"
must have a score of 0 for that to happen.

This was actually affecting bitmap fonts (in a bad way), as the change made
an outline font to always be preferred over a (otherwise equal) bitmap font,
even for the exact size of the bitmap font.  That probably was never noticed
by anyone, but with the font range support this has become clear (and worked
around by Akira).  To clean that up, I'm reverting this so I can land the
rest of patches for bug 80873.

https://bugs.freedesktop.org/show_bug.cgi?id=80873#c10