changes file and docs for 18640.

changes/18640

+  o Major features (resource management):
+    - Tor now includes support for noticing when we are about to run out of
+      sockets, and preemptively closing connections of lower priority.
+      (This feature is off by default for now, since the current prioritizing
+      method is not mature enough yet. You can enable it by setting
+      "DisableOOSCheck 0".) Closes ticket 18640.

doc/tor.1.txt

@@ -2041,6 +2041,12 @@ is non-zero):
     this.  If this option is set to 0, Tor will try to pick a reasonable
     default based on your system's physical memory.  (Default: 0)
 
+[[DisableOOSCheck]] **DisableOOSCheck** **0**|**1**::
+    This option disables the code that closes connections when Tor notices
+    that it is running low on sockets. Right now, it is on by default,
+    since the existing out-of-sockets mechanism tends to kill OR connections
+    more than it should. (Default: 1)
+
 [[SigningKeyLifetime]] **SigningKeyLifetime** __N__ **days**|**weeks**|**months**::
     For how long should each Ed25519 signing key be valid?  Tor uses a
     permanent master identity key that can be kept offline, and periodically