Small ringtone plugin fixes

Remove unneeded check from checksum plugin

Add shuffle to mocplay

Remove duplicate code (#295)

These three lines are exact copy of 4555-4557.
As opener is not changed in between, we can delete these

Set CP in Makefile

$(CP) is not set by GNU Make
Seems like [1] is a full list of what GNU Make defines implicitly
[1] https://www.gnu.org/software/make/manual/html_node/Implicit-Variables.html

Added md5sum plugin

Add clarification for usage of moving and copying selections

Fix sign conversion and comparison warnings

Don't ignore fwrite errors

Fixes warning on CentOS 6:

  src/nnn.c:754: warning: ignoring return value of 'fwrite', declared with attribute warn_unused_result

Building on i386 (NetBSD or Debian):

  src/nnn.c: In function 'selectiontofd':
  src/nnn.c:783:13: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
    while (pos <= lastpos) {
               ^
  src/nnn.c:791:11: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     if (pos <= lastpos) {
             ^
  src/nnn.c: In function 'showcplist':
  src/nnn.c:823:17: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
    if (pos && pos == copybufpos)
                   ^
  src/nnn.c: In function 'xlink':
  src/nnn.c:1955:13: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
    while (pos < copybufpos) {