Get some of the last remaining C files into C++

They still need to be fixed up, but they now build with C++.

dpid/misc_new.hh

@@ -0,0 +1,18 @@
+#ifndef MISC_NEW_H
+#define MISC_NEW_H
+
+#ifdef __cplusplus
+extern "C"
+{
+#endif
+
+Dstr *a_Misc_rdtag(int socket);
+char *a_Misc_readtag(int sock);
+char *a_Misc_mkdtemp(char *template_);
+char *a_Misc_mkfname(char *template_);
+char *a_Misc_mksecret(int nchar);
+
+#ifdef __cplusplus
+}
+#endif
+#endif