Retarget git modules at github.

.gitmodules

 [submodule "bpl-subset"]
 	path = bpl-subset
-	url = http://git.tiker.net/trees/bpl-subset.git
+	url = git://github.com/inducer/bpl-subset.git
 [submodule "pyopencl/compyte"]
 	path = pyopencl/compyte
-	url = http://git.tiker.net/trees/compyte.git
+	url = git://github.com/inducer/compyte.git