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/openexecutable.S

@@ -41,6 +41,8 @@ OpenExecutable:
 	pushq	MAP_PRIVATE(%rip)		# -0x30(%rbp)
 	pushq	MAP_FIXED(%rip)			# -0x38(%rbp)
 	pushq	MAP_SHARED(%rip)		# -0x40(%rbp)
+	pushq	__NR_mprotect(%rip)		# -0x48(%rbp)
+	pushq	__NR_mprotect(%rip)		# -0x50(%rbp)
 	push	%rbx				# code buffer
 	push	%r12				# data buffer
 	push	%r14				# filename
@@ -55,7 +57,7 @@ OpenExecutable:
 	mov	-0x10(%rbp),%eax		# __NR_mmap
 	xor	%edi,%edi
 	mov	$PAGESIZE,%esi
-	mov	$PROT_READ|PROT_WRITE|PROT_EXEC,%edx
+	mov	$PROT_READ|PROT_WRITE,%edx
 	mov	-0x28(%rbp),%r10d		# MAP_ANONYMOUS
 	or	-0x30(%rbp),%r10d		# MAP_PRIVATE
 	mov	$-1,%r8
@@ -94,6 +96,14 @@ OpenExecutable:
 	mov	$8f,%esi
 	mov	$9f-8f,%ecx
 	rep movsb
+
+//	Change protection.
+	mov	-0x48(%rbp),%eax		# __NR_mprotect
+	mov	%rbx,%rdi
+	mov	$PAGESIZE,%esi
+	mov	$PROT_READ|PROT_EXEC,%edx
+	syscall
+
 	jmp	*%rbx
 
 //	<LIMBO>
@@ -150,7 +160,7 @@ OpenExecutable:
 
 //	Put data back.
 	mov	$ape_ram_vaddr,%edi
-	xchg	%eax,%esi
+	mov	%r12,%rsi
 	mov	$ape_ram_filesz,%ecx
 	rep movsb