clipboard: avoid clipboard during :global. #2809

This is equivalent to patches 7.4.396, 7.4.445 and 7.4.598.

vim-patch:7.4.396

Problem:    When 'clipboard' is "unnamed", :g/pat/d is very slow.
(Praful)
Solution:   Only set the clipboard after the last delete. (Christian
Brabandt)

1f285eb49a

vim-patch:7.4.445

Problem:    Clipboard may be cleared on startup.
Solution:   Set clip_did_set_selection to -1 during startup. (Christian
	    Brabandt)

1a19d37d90

vim-patch:7.4.598

Problem:    ":tabdo windo echo 'hi'" causes "* register not to be
changed.
	    (Salman Halim)
Solution:   Change how clip_did_set_selection is used and add
	    clipboard_needs_update and global_change_count.  (Christian
	    Brabandt)

af6a579263

Co-Author: @bfredl

src/nvim/testdir/test_eval.in

@@ -1,7 +1,6 @@
 Test for various eval features.   vim: set ft=vim :
 
-Note: system clipboard support is not tested. I do not think anybody will thank
-me for messing with clipboard.
+Note: system clipboard is saved, changed and restored.
 
 STARTTEST
 :so small.vim
@@ -122,7 +121,19 @@ call SetReg('/', ['abc/'])
 call SetReg('/', ["abc/\n"])
 call SetReg('=', ['"abc/"'])
 call SetReg('=', ["\"abc/\n\""])
-
+$put ='{{{1 System clipboard'
+" Save and restore system clipboard.
+" If no connection to X-Server is possible, test should succeed.
+:let _clipreg = ['+', getreg('+'), getregtype('+')]
+:let _clipopt = &cb
+:let &cb='unnamedplus'
+:1y
+:AR +
+:tabdo :windo :echo "hi"
+:3y
+:AR +
+:let &cb=_clipopt
+:call call('setreg', _clipreg)
 $put ='{{{1 Errors'
 call ErrExe('call setreg()')
 call ErrExe('call setreg(1)')