mobject will need "self-forward" feature

Updated mercury to provide a "self-forward" variant.  Updated mobject to
depend on this verison plus a few other packages it now needs.

packages/mercury/package.py

@@ -37,6 +37,7 @@ class Mercury(CMakePackage):
     variant('cci', default=False, description="Use CCI for network transport")
     variant('bmi', default=False, description="Use BMI for network transport")
     variant('fabric',default=True, description="Use libfabric for net transport")
+    variant('selfforward', default=False, description="Mercury will short-circuit operations by forwarding to itself when possible")
 
     # if nothing specified, build good ol' BMI
     depends_on('cci@master', when="+cci", type=("build", "link", "run"))
@@ -54,5 +55,7 @@ class Mercury(CMakePackage):
 		args.extend(["-DNA_USE_BMI:BOOL=ON"])
 	if (self.spec.variants['fabric'].value):
 		args.extend(["-DNA_USE_OFI:BOOL=ON"])
+        if (self.spec.variants['selfforward'].value):
+                args.extend(["-DMERCURY_USE_SELF_FORWARD=ON"])
 
         return args

packages/mobject/package.py

@@ -33,7 +33,15 @@ class Mobject(AutotoolsPackage):
 
     version('master', git='https://xgitlab.cels.anl.gov/sds/mobject-store.git')
     depends_on('margo')
-    depends_on('ssg')
+    depends_on('mpi')
+    depends_on('ssg+mpi')
     depends_on('autoconf')
     depends_on('automake')
     depends_on('libtool')
+    depends_on('sdskeyval')
+    depends_on('bake-bulk')
+    depends_on('mercury+selfforward')
+
+    def configure_args(self):
+        extra_args = ['CC=%s' % self.spec['mpi'].mpicc]
+        return extra_args