libbb: new option FEATURE_ETC_SERVICES: if off, /etc/services reads often avoided

In practice, "wget http://host.com/" always uses port 80.
People explicitly set non-standard ports via options or parameters
("telnet 1.2.3.4 567" or "telnet 1.2.3.4 ftp") instead of modifying
/etc/services.

function                                             old     new   delta
telnet_main                                         1466    1464      -2
rdate_main                                           215     198     -17
fakeidentd_main                                      269     252     -17
parse_url                                            459     392     -67
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 0/4 up/down: 0/-103)           Total: -103 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
diff --git a/libbb/Config.src b/libbb/Config.src
index fdf8bbb..16e1648 100644
--- a/libbb/Config.src
+++ b/libbb/Config.src
@@ -76,6 +76,18 @@
 	a rarely used feature which allows you to use names
 	instead of IP/mask pairs in route command.
 
+config FEATURE_ETC_SERVICES
+	bool "Consult /etc/services even for well-known ports"
+	default n
+	help
+	Look up e.g. "telnet" and "http" in /etc/services file
+	instead of assuming ports 23 and 80.
+	This is almost never necessary (everybody uses standard ports),
+	and it makes sense to avoid reading this file.
+	If you disable this option, in the cases where port is explicitly
+	specified as a service name (e.g. "telnet HOST PORTNAME"),
+	it will still be looked up in /etc/services.
+
 config FEATURE_EDITING
 	bool "Command line editing"
 	default y