Add an option "-J" / "--pipe-buffer-size" to set the size of the output pipe buffer when the output is a pipe, and when that option is not specified, automatically increase the output pipe buffer size to match that of the input, when the first input is also a pipe (#188).

docs/pv.1

@@ -291,6 +291,14 @@ automatically switches on \*(lq\fB\-\-no\-splice\fR\*(rq.
 Switching on this option results in a small loss of transfer efficiency.
 It has no effect on systems where \fBsplice\fR(2) is unavailable.
 .TP
+.BI \-J\  BYTES \fR,\ \fB\-\-pipe\-buffer\-size\  BYTES
+Attempt to set the size of the output pipe buffer to \fIBYTES\fR bytes.
+This will only have an effect if the output is a pipe, and will silently do
+nothing if the requested size cannot be achieved.
+If this option is not specified, and both the output and the first input are
+pipes, then the output pipe buffer size will automatically be increased to
+match the input pipe buffer, if it was smaller.
+.TP
 .B \-E, \-\-skip-errors
 Ignore read errors by attempting to skip past the offending sections.
 The corresponding parts of the output will be null bytes.
@@ -857,10 +865,10 @@ effective with small input files, and \*(lq\fB%nL\fR\*(rq may be a few lines
 out due to buffering within the pipeline itself.
 .PP
 Numbers passed to \*(lq\fB\-\-size\fR\*(rq, \*(lq\fB\-\-rate\-limit\fR\*(rq,
-\*(lq\fB\-\-buffer\-size\fR\*(rq, and \*(lq\fB\-\-error\-skip\-block\fR\*(rq
-may all be expressed as decimals if followed by a suffix, so for example
-\*(lq\fI\-\-size\~1.5G\fR\*(rq is equivalent to
-\*(lq\fI\-\-size\~1536M\fR\*(rq.
+\*(lq\fB\-\-buffer\-size\fR\*(rq, \*(lq\fB\-\-pipe\-buffer\-size\fR\*(rq,
+and \*(lq\fB\-\-error\-skip\-block\fR\*(rq may all be expressed as decimals
+if followed by a suffix, so for example \*(lq\fI\-\-size\~1.5G\fR\*(rq is
+equivalent to \*(lq\fI\-\-size\~1536M\fR\*(rq.
 .PP
 Numbers passed to \*(lq\fB\-\-interval\fR\*(rq and
 \*(lq\fB\-\-delay\-start\fR\*(rq may be integers or decimals, but may not