Options::wal_dir shouldn't end in '/'

Summary: If a client specifies wal_dir with trailing '/', we will fail in deleting obsolete log files. See task #4083746

Test Plan: make check

Reviewers: haobo, sdong

Reviewed By: haobo

CC: leveldb

Differential Revision: https://reviews.facebook.net/D17535

db/db_impl.cc

@@ -322,6 +322,9 @@ Options SanitizeOptions(const std::string& dbname,
     // Use dbname as default
     result.wal_dir = dbname;
   }
+  if (result.wal_dir.back() == '/') {
+    result.wal_dir = result.wal_dir.substr(result.wal_dir.size() - 1);
+  }
 
   // -- Sanitize the table properties collector
   // All user defined properties collectors will be wrapped by