clean up previous commit

- suggested by Todd Gamblin.  There are two depends_on() statements now.
  The second one will only be triggered on cray platform, and will be merged
  with prevous depends_on

packages/mercury/package.py

@@ -42,7 +42,8 @@ class Mercury(CMakePackage):
 
     # if nothing specified, build good ol' BMI
     depends_on('cci@master', when="+cci", type=("build", "link", "run"))
-    depends_on('libfabric@develop', when="+fabric", type=("build", "link", "run"))
+    depends_on('libfabric', when="+fabric", type=("build", "link", "run"))
+    depends_on('libfabric@develop', when="+fabric platform=cray", type=("build", "link", "run"))
     depends_on('bmi', when="+bmi", type=("build", "link", "run"))
     depends_on('openpa', type=("build", "link", "run"))