Allow loading tools.xml from mirror *or* s.b.e
Allow loading tools.xml from mirror *or* s.b.e

Using full http://s.b.e/snapsource/tools.xml disallows local repository.
Using relative tools.xml disallows running from local disk but getting tools from s.b.e.
So we try both.
ericrosenbaum/BeetleBlocks,jmoenig/Snap--Build-Your-Own-Blocks,ericrosenbaum/BeetleBlocks,jmoenig/Snap--Build-Your-Own-Blocks