Indentation seems broken
I am currently missing the indend between filename and result in benchexecs output: 

````
monteverdi UAutomizer-linux # ../../../../benchexec/bin/benchexec ../benchexec/benchexec-automizer-small.xml --no-container --no-compress-results

executing run set 'Test.CFI'     (5 files)
08:00:58   ../../../trunk/examples/svcomp/ssh-simplified/s3_clnt_1_true-unreach-call.cil.cTIMEOUT                  60.12   33.63
08:01:33   ../../../trunk/examples/svcomp/ssh-simplified/s3_clnt_1_false-unreach-call.cil.cfalse(unreach-call)      27.52   14.31
08:01:47   ../../../trunk/examples/svcomp/loop-acceleration/array_true-unreach-call3_true-termination.itrue                     11.16    5.81
08:01:53   ../../../trunk/examples/svcomp/loop-acceleration/simple_false-unreach-call2_true-termination.ifalse(unreach-call)       6.69    3.45
08:01:57   ../../../trunk/examples/svcomp/loop-acceleration/multivar_true-unreach-call1_true-termination.itrue                      7.08    3.38
[...]
````

For me, it still worked on c2388e740d39bb5b9fc002cce4f75679d72c94a5
diff --git a/benchexec/outputhandler.py b/benchexec/outputhandler.py
index 9c3c3d84..6459dbed 100644
--- a/benchexec/outputhandler.py
+++ b/benchexec/outputhandler.py
@@ -284,10 +284,12 @@ class OutputHandler(object):
         """
         xml_file_name = self.get_filename(runSet.name, "xml")
 
-        identifier_names = [util.relative_path(run.identifier, xml_file_name) for run in runSet.runs]
+        identifier_names = [run.identifier for run in runSet.runs]
 
         # common prefix of file names
-        runSet.common_prefix = util.common_base_dir(identifier_names) + os.path.sep
+        runSet.common_prefix = util.common_base_dir(identifier_names)
+        if runSet.common_prefix:
+            runSet.common_prefix += os.path.sep
 
         # length of the first column in terminal
         runSet.max_length_of_filename = max(len(file) for file in identifier_names) if identifier_names else 20
['benchexec/outputhandler.py']