Add /statusz page to redbean plus other enhancements

redbean improvements:

- Explicitly disable corking
- Simulate Python regex API for Lua
- Send warmup requests in main process on startup
- Add Class-A granular IPv4 network classification
- Add /statusz page so you can monitor your redbean's health
- Fix regressions on OpenBSD/NetBSD caused by recent changes
- Plug Authorization header into Lua GetUser and GetPass APIs
- Recognize X-Forwarded-{For,Host} from local reverse proxies
- Add many additional functions to redbean Lua server page API
- Report resource usage of child processes on `/` listing page
- Introduce `-a` flag for logging child process resource usage
- Introduce `-t MILLIS` flag and `ProgramTimeout(ms)` init API
- Introduce `-H "Header: value"` flag and `ProgramHeader(k,v)` API

Cosmopolitan Libc improvements:

- Make strerror() simpler
- Make inet_pton() not depend on sscanf()
- Fix OpenExecutable() which broke .data section earlier
- Fix stdio in cases where it overflows kernel tty buffer
- Fix bugs in crash reporting w/o .com.dbg binary present
- Add polyfills for SO_LINGER, SO_RCVTIMEO, and SO_SNDTIMEO
- Polyfill TCP_CORK on BSD and XNU using TCP_NOPUSH magnums

New netcat clone in examples/nc.c:

While testing some of the failure conditions for redbean, I noticed that
BusyBox's `nc` command is pretty busted, if you use it as an interactive
tool, rather than having it be part of a pipeline. Unfortunately this'll
only work on UNIX since Windows doesn't let us poll on stdio and sockets
at the same time because I don't think they want tools like this running
on their platform. So if you want forbidden fruit, it's here so enjoy it

libc/runtime/finddebugbinary.c

@@ -29,40 +29,28 @@
 /**
  * Returns path of binary with the debug information, or null.
  *
- * @return path to debug binary, or -1 w/ errno
+ * @return path to debug binary, or NULL
  */
 const char *FindDebugBinary(void) {
-  unsigned i, len;
-  char buf[2][PATH_MAX];
-  static char res[PATH_MAX];
-  const char *bins[4], *pwd, *comdbg;
-  if (res[0]) return res;
-  if ((comdbg = emptytonull(getenv("COMDBG")))) return comdbg;
-  if (res[0]) return res;
-  bins[0] = program_invocation_name;
-  bins[1] = (const char *)getauxval(AT_EXECFN);
-  pwd = emptytonull(getenv("PWD"));
-  for (i = 0; i < 2; ++i) {
-    if (pwd && bins[i] && bins[i][0] != '/' && bins[i][0] != '\\' &&
-        strlen(pwd) + 1 + strlen(bins[i]) + 1 <= ARRAYLEN(buf[0])) {
-      strcpy(buf[i], pwd);
-      strcat(buf[i], "/");
-      strcat(buf[i], bins[i]);
-      bins[i + 2] = buf[i];
+  static bool once;
+  static char *res;
+  static char buf[PATH_MAX + 1];
+  char *p;
+  size_t n;
+  if (!once) {
+    if (!(res = getenv("COMDBG"))) {
+      p = (char *)getauxval(AT_EXECFN);
+      n = strlen(p);
+      if (n > 4 && !memcmp(p + n - 4, ".dbg", 4)) {
+        res = p;
+      } else if (n + 4 <= PATH_MAX) {
+        mempcpy(mempcpy(buf, p, n), ".dbg", 5);
+        if (fileexists(buf)) {
+          res = buf;
+        }
+      }
     }
+    once = true;
   }
-  for (i = 0; i < 4; ++i) {
-    if (!bins[i]) continue;
-    len = strlen(bins[i]);
-    memcpy(res, bins[i], len + 1);
-    if (!endswith(res, ".dbg") && len + 3 + 1 <= ARRAYLEN(res)) {
-      strcat(res, ".dbg");
-    }
-    if (fileexists(res)) {
-      return res;
-    }
-  }
-  res[0] = '\0';
-  errno = ENOENT;
-  return NULL;
+  return res;
 }