Move set_metadata (once again), to galaxy_ext so that the galaxy

namespace does not conflict with others (e.g. the galaxy-ops package in
the toolshed).

lib/galaxy/datatypes/metadata.py

@@ -777,10 +777,10 @@ class JobExternalOutputMetadataWrapper( object ):
             #return command required to build
             fd, fp = tempfile.mkstemp( suffix='.py', dir = tmp_dir, prefix = "set_metadata_" )
             metadata_script_file = abspath( fp )
-            os.fdopen( fd, 'w' ).write( 'from galaxy.metadata.set_metadata import set_metadata; set_metadata()' )
+            os.fdopen( fd, 'w' ).write( 'from galaxy_ext.metadata.set_metadata import set_metadata; set_metadata()' )
             return "python %s %s" % ( metadata_path_on_compute(metadata_script_file), args )
         else:
-            # return args to galaxy.metadata.set_metadata required to build
+            # return args to galaxy_ext.metadata.set_metadata required to build
             return args
 
     def external_metadata_set_successfully( self, dataset, sa_session ):

lib/galaxy/datatypes/registry.py

@@ -660,7 +660,7 @@ class Registry( object ):
                 <param name="__SET_EXTERNAL_METADATA_COMMAND_LINE__" type="hidden" value=""/>
               </inputs>
               <configfiles>
-                <configfile name="set_metadata">from galaxy.metadata.set_metadata import set_metadata; set_metadata()</configfile>
+                <configfile name="set_metadata">from galaxy_ext.metadata.set_metadata import set_metadata; set_metadata()</configfile>
               </configfiles>
             </tool>
             """

lib/galaxy_ext/__init__.py

@@ -0,0 +1,4 @@
+""" Package for things which are loaded from outside Galaxy and which we can be
+sure will not conflict with the `galaxy` namespace, which may be provided by
+other packages (e.g. galaxy_ops in the toolshed).
+"""