Re-dangle requirements.txt for branches of pyopencl, loopy, and pytential

requirements.txt

 numpy
 git+https://gitlab.tiker.net/inducer/gmsh_interop.git
 git+https://gitlab.tiker.net/inducer/modepy.git
-git+https://gitlab.tiker.net/inducer/pyopencl.git
+git+https://gitlab.tiker.net/inducer/pyopencl.git@better-empty-handling
 git+https://gitlab.tiker.net/inducer/islpy.git
 
 
@@ -9,12 +9,12 @@ git+https://gitlab.tiker.net/inducer/islpy.git
 git+https://gitlab.tiker.net/inducer/pymbolic.git
 
 # also depends on pymbolic, so should come after it
-git+https://gitlab.tiker.net/inducer/loopy.git
+git+https://gitlab.tiker.net/inducer/loopy.git@empty-ndrange-enqueue
 
 # more pytential dependencies
 git+https://gitlab.tiker.net/inducer/boxtree.git
 git+https://gitlab.tiker.net/inducer/sumpy.git
-git+https://gitlab.tiker.net/inducer/pytential.git
+git+https://gitlab.tiker.net/inducer/pytential.git@array-context
 
 # requires pymetis for tests for partition_mesh
 git+https://gitlab.tiker.net/inducer/pymetis.git