merged 'develop' into 'test_suite' and resolved conflicts

docs/source/quickinstall.rst

@@ -43,6 +43,7 @@ following commands in a terminal:
 
     git clone git://github.com/mit-crpg/openmc.git
     cd openmc/src
+    git checkout master
     make
     sudo make install
 

docs/source/usersguide/install.rst

@@ -102,6 +102,12 @@ repository::
 
     git clone git://github.com/mit-crpg/openmc.git
 
+By default, the cloned repository will be set to the development branch. To
+switch to the source of the latest stable release, run the following commands::
+
+    cd openmc/src
+    git checkout master
+
 .. _GitHub: https://github.com/mit-crpg/openmc
 .. _git: http://git-scm.com
 .. _ssh: http://en.wikipedia.org/wiki/Secure_Shell

tests/test_survival_biasing/materials.xml

@@ -2,8 +2,9 @@
 <materials>
 
   <material id="1">
-    <density value="4.5" units="g/cc" />
-    <nuclide name="U-235" xs="70c" ao="1.0" />
+    <density value="19.5" units="g/cc" />
+    <nuclide name="U-235" xs="70c" ao="2.0" />
+    <nuclide name="U-238" xs="70c" ao="1.0" />
   </material>
 
 </materials>

tests/test_survival_biasing/results_true.dat

@@ -1,2 +1,2 @@
 k-combined:
-3.048732E-01 9.834003E-03
+9.688077E-01 6.981246E-02