cairo snapshot 1.5.20 now available

This is the tenth snapshot in cairo's unstable 1.5 series. It comes just two days (and only one working day) after the 1.5.18 snapshot. The quick snapshot is due to two embarrassing bugs (both affecting cairo-xlib) that had been introduced in the 1.5.18 snapshot. The fixes for these are described below along with a few other fixes, (which hopefully aren't introducing new bugs this time).

We're hopeful that this release candidate holds up better than the last one, and that we'll be able to make a 1.6.0 release soon with no major code changes from this snapshot.