Avoid error output from git update check

mpcdf_common.py

@@ -52,7 +52,7 @@ def check_for_update():
     import os
     import sys
     import time
-    from subprocess import check_output, call
+    from subprocess import check_output, call, DEVNULL
 
     if hasattr(sys.modules["mpcdf_common"], "checked_for_updates"):
         return
@@ -88,7 +88,7 @@ def check_for_update():
     with open(rev_file, "r") as fd:
         server_rev = fd.read().strip()
 
-    if call(["git", "--git-dir", git_dir, "merge-base", "--is-ancestor", server_rev, "HEAD"]) == 0:
+    if call(["git", "--git-dir", git_dir, "merge-base", "--is-ancestor", server_rev, "HEAD"], stderr=DEVNULL) == 0:
         # Server rev is older than ours. Check again
         update_server_rev()
 
@@ -97,7 +97,7 @@ def check_for_update():
 
     if server_rev != local_rev:
         print("Note from MPCDF osc plugins:", file=sys.stderr)
-        if call(["git", "--git-dir", git_dir, "merge-base", "--is-ancestor", server_rev, "HEAD"]) == 0:
+        if call(["git", "--git-dir", git_dir, "merge-base", "--is-ancestor", server_rev, "HEAD"], stderr=DEVNULL) == 0:
             print(" You have unpushed commits in", plugin_dir, "- consider pushing them", file=sys.stderr)
             print(file=sys.stderr)
         else: