Update extensions.lua.sample with naming conflict guidance.

The sample extensions.lua was causing pbx_lua to fail to load when parsing
'app.goto("default", "s", 1)' because in Lua 5.2, 'goto' is now a reserved
word.  This patch adds guidance to extensions.lua.sample and changed
'app.goto("default", "s", 1)' to 'app.['goto']("default", "s", 1)'. 

ASTERISK-23844 #close
Reported by: rnewton
Tested by: gtjoseph
Review: https://reviewboard.asterisk.org/r/3627/
 
........

Merged revisions 416581 from http://svn.asterisk.org/svn/asterisk/branches/11


git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/12@416582 65c4cc65-6c06-0410-ace0-fbb531ad65f3

configs/extensions.lua.sample

@@ -85,6 +85,7 @@ TRUNKMSD = 1
 --
 --    app.Dial("DAHDI/1")
 --    app.dial("DAHDI/1")
+--    app["dial"]("DAHDI/1")
 --
 -- More examples can be found below.
 --
@@ -97,6 +98,24 @@ TRUNKMSD = 1
 -- check the current status of the autoservice and will return true if an
 -- autoservice is currently running.
 --
+-- Note about naming conflicts:
+-- Lua allows you to refer to table entries using the '.' notation,
+-- I.E. app.goto(something), only if the entry doesn't conflict with an Lua
+-- reserved word.  In the 'goto' example, with Lua 5.1 or earlier, 'goto' is
+-- not a reserved word so you'd be calling the Asterisk dialplan application
+-- 'goto'.  Lua 5.2 however, introduced the 'goto' control statement which
+-- makes 'goto' a reserved word.  This casues the interpreter to fail parsing
+-- the file and pbx_lua.so will fail to load.  The same applies to any use of
+-- Lua tables including extensions, channels and any tables you create.
+--
+-- There are two ways around this:  Since Lua is case-sensitive, you can use
+-- capitalized names, I.E. app.Goto(something) to refer to the Asterisk apps,
+-- functions, etc. Or you can use the full syntax, I.E. app["goto"](something).
+-- Both syntaxes are backwards compatible with earlier Lua versions.  To make
+-- your Lua dialplans easier to maintain and to reduce the chance of future
+-- conflicts you may want to use the app["goto"](something) syntax for all
+-- table accesses.
+--
 
 function outgoing_local(c, e)
 	app.dial("DAHDI/1/" .. e, "", "")
@@ -144,7 +163,8 @@ extensions = {
 		end;
 
 		["1000"] = function()
-			app.goto("demo", "s", 1)
+--	See the naming conflict note above.
+			app['goto']("default", "s", 1)
 		end;
 
 		["1234"] = function()