Update the usage examples in match.lua

The example uses of nmap.receive_buf() were missing the second
parameter, keeppattern. Also referenced the match library from
nmap.receive_buf's NSEdoc to avoid reimplementations of buffered
sockets.

nselib/match.lua

@@ -12,11 +12,11 @@ _ENV = stdnse.module("match", stdnse.seeall)
 --various functions for use with nse's nsock:receive_buf - function
 
 -- e.g.
--- sock:receive_buf(regex("myregexpattern")) - does a match using pcre- regular-
---                                           - expressions
--- sock:receive_buf(numbytes(80)) - is the buffered version of
---                                  sock:receive_bytes(80) - i.e. it returns
---                                  exactly 80 bytes and no more
+-- sock:receive_buf(regex("myregexpattern"), true) - does a match using pcre
+--                                                   regular expressions
+-- sock:receive_buf(numbytes(80), true) - is the buffered version of
+--                                        sock:receive_bytes(80) - i.e. it
+--                                        returns exactly 80 bytes and no more
 
 --- Return a function that allows delimiting with a regular expression.
 --
@@ -24,7 +24,7 @@ _ENV = stdnse.module("match", stdnse.seeall)
 -- give script developers the ability to use regular expressions for delimiting
 -- instead of Lua's string patterns.
 -- @param pattern The regex.
--- @usage sock:receive_buf(match.regex("myregexpattern"))
+-- @usage sock:receive_buf(match.regex("myregexpattern"), true)
 -- @see nmap.receive_buf
 -- @see pcre.exec
 regex = function(pattern)
@@ -42,8 +42,12 @@ end
 -- <code>sock:receive_bytes(n)</code> in case a script requires more than one
 -- fixed-size chunk, as the unbuffered version may return more bytes than
 -- requested and thus would require you to do the parsing on your own.
+--
+-- The <code>keeppattern</code> parameter to receive_buf should be set to
+-- <code>true</code>, otherwise the string returned will be 1 less than
+-- <code>num</code>
 -- @param num Number of bytes.
--- @usage sock:receive_buf(match.numbytes(80))
+-- @usage sock:receive_buf(match.numbytes(80), true)
 -- @see nmap.receive_buf
 numbytes = function(num)
   local n = num