static_assert that Iterator is conformant bidi iterator

VersionedMap.cpp

@@ -21,6 +21,8 @@
 bool debugVerboseEnabled = true;
 #endif
 
+static_assert(std::bidirectional_iterator<weaselab::VersionedMap::Iterator>);
+
 void *mmapSafe(void *addr, size_t len, int prot, int flags, int fd,
                off_t offset) {
   void *result = mmap(addr, len, prot, flags, fd, offset);