Make wget capable of starting downloads from a specified position.

This patch adds an option `--start-pos' for specifying starting position
of a HTTP or FTP download.

Signed-off-by: Yousong Zhou <yszhou4tech@gmail.com>

doc/ChangeLog

@@ -1,3 +1,7 @@
+2014-02-10  Yousong Zhou  <yszhou4tech@gmail.com>
+
+	* wget.texi: Add documentation for --start-pos.
+
 2013-12-29  Giuseppe Scrivano  <gscrivan@redhat.com>
 
 	* wget.texi: Update to GFDL 1.3.

doc/wget.texi

@@ -701,6 +701,22 @@ Another instance where you'll get a garbled file if you try to use
 Note that @samp{-c} only works with @sc{ftp} servers and with @sc{http}
 servers that support the @code{Range} header.
 
+@cindex offset
+@cindex continue retrieval
+@cindex incomplete downloads
+@cindex resume download
+@cindex start position
+@item --start-pos=@var{OFFSET}
+Start downloading at zero-based position @var{OFFSET}.  Offset may be expressed
+in bytes, kilobytes with the `k' suffix, or megabytes with the `m' suffix, etc.
+
+@samp{--start-pos} has higher precedence over @samp{--continue}.  When
+@samp{--start-pos} and @samp{--continue} are both specified, wget will emit a
+warning then proceed as if @samp{--continue} was absent.
+
+Server support for continued download is required, otherwise @samp{--start-pos}
+cannot help.  See @samp{-c} for details.
+
 @cindex progress indicator
 @cindex dot style
 @item --progress=@var{type}