Add a heuristic to skip git checkouts not managed by crup

crup-runner.sh

Index: crup-runner.sh
diff --git a/crup-runner.sh b/crup-runner.sh
index 987dcc2939f6556686ff1746cbc681fa5e737f15..b82206727f65583b8c0170c5381f7e6c2505b713 100755
--- a/crup-runner.sh
+++ b/crup-runner.sh
@@ -64,6 +64,12 @@ solution="${1%%/*}"
 cd "$solution"
 
 if [ "$solution" = "$1" ]; then
+  # Skip git checkouts not managed by crup.
+  if ! grep -q -s "The Chromium Authors" ".git/description"; then
+    echo "Skipping unmanaged git directory $1" 1>&2
+    exit 0
+  fi
+
   # Don't "pull" if checkout is not on a named branch
   shift
   if test "$2" = "pull" && ( ! git symbolic-ref HEAD >/dev/null 2>/dev/null ); then