Deduplication of backend list

Fixes issue #609. Added backend list debug output (class name).

tools/sigma/backends/discovery.py

@@ -25,7 +25,7 @@ from sigma.tools import getAllSubclasses, getClassDict
 def getBackendList():
     """Return list of backend classes"""
     path = os.path.dirname(__file__)
-    return getAllSubclasses(path, "backends", BaseBackend)
+    return frozenset(getAllSubclasses(path, "backends", BaseBackend))
 
 def getBackendDict():
     return getClassDict(getBackendList())

tools/sigmac

@@ -126,7 +126,10 @@ if cmdargs.debug:   # pragma: no cover
 
 def list_backends():
     for backend in backends.getBackendList():
-        print("{:>15} : {}".format(backend.identifier, backend.__doc__))
+        if cmdargs.debug:
+            print("{:>15} : {} ({})".format(backend.identifier, backend.__doc__, backend.__name__))
+        else:
+            print("{:>15} : {}".format(backend.identifier, backend.__doc__))
 
 def list_configurations(backend=None):
     for conf_id, title, backends in scm.list():