promise? and force a bit, describe recursive forcing of a promise by
its own code.
+ * scheme-io.texi (Ports): Add notes on garbage collection, and on
+ explicitly closing file ports.
+ (File Ports): Cross reference Ports node on explicit closing.
+
+ * posix.texi (Network Sockets and Communication): Cross reference
+ Ports node on explicit closing.
+
* scheme-scheduling.texi (Futures): New section.
* srfi-modules.texi (SRFI-13 Miscellaneous): In string-replace, note