[$] 5.1 Merge window part 2

By the time that 5.1-rc1 was released andthe 5.1 merge window ended, 11,241 non-merge changesets had been pulled into the mainline repository. Of those, just over 5,000 werepulled since the first 5.1 merge-windowsummary. It often happens that the biggest changes are pulledearly, with the emphasis shifting to fixes by the end of the mergewindow; this time, though, some of the most significant features were savedfor last.