vim-patch:8.1.1483: skipped tests are not properly listed

Problem:    Skipped tests are not properly listed.
Solution:   Throw a "Skipped" exception instead of using ":finish" or ":return".
5d30ff1964

Skips quite some (N/A) tests.

vim-patch:8.1.0503: missing change to diff test (included in cf1ffa916)

src/nvim/testdir/test_breakindent.vim

@@ -5,7 +5,7 @@
 " It helps to change the tabstop setting and force a redraw (e.g. see
 " Test_breakindent08())
 if !exists('+breakindent')
-  finish
+  throw 'Skipped: breakindent option not supported'
 endif
 
 source view_util.vim

src/nvim/testdir/test_clientserver.vim

@@ -1,7 +1,7 @@
 " Tests for the +clientserver feature.
 
 if !has('job') || !has('clientserver')
-  finish
+  throw 'Skipped: job and/or clientserver feature missing'
 endif
 
 source shared.vim

src/nvim/testdir/test_debugger.vim

@@ -22,7 +22,7 @@ endfunc
 " Debugger tests
 func Test_Debugger()
   if !CanRunVimInTerminal()
-    return
+    throw 'Skipped: cannot run Vim in a terminal window'
   endif
 
   " Create a Vim script with some functions

src/nvim/testdir/test_diffmode.vim

@@ -723,7 +723,7 @@ endfunc
 
 func Test_diff_with_cursorline()
   if !CanRunVimInTerminal()
-    return
+    throw 'Skipped: cannot run Vim in a terminal window'
   endif
 
   call writefile([
@@ -750,7 +750,7 @@ endfunc
 
 func Test_diff_of_diff()
   if !CanRunVimInTerminal()
-    return
+    throw 'Skipped: cannot run Vim in a terminal window'
   endif
   if !has("rightleft")
     throw 'Skipped: rightleft not supported'

src/nvim/testdir/test_fold.vim

@@ -706,7 +706,7 @@ endfunc
 
 func Test_folds_with_rnu()
   if !CanRunVimInTerminal()
-    return
+    throw 'Skipped: cannot make screendumps'
   endif
 
   call writefile([

src/nvim/testdir/test_highlight.vim

@@ -532,7 +532,7 @@ endfunc
 
 func Test_cursorline_after_yank()
   if !CanRunVimInTerminal()
-    return
+    throw 'Skipped: cannot make screendumps'
   endif
 
   call writefile([
@@ -554,7 +554,7 @@ endfunc
 
 func Test_cursorline_with_visualmode()
   if !CanRunVimInTerminal()
-    return
+    throw 'Skipped: cannot make screendumps'
   endif
 
   call writefile([

src/nvim/testdir/test_search.vim

@@ -496,7 +496,7 @@ func Test_incsearch_substitute_dump()
     return
   endif
   if !CanRunVimInTerminal()
-    return
+    throw 'Skipped: cannot make screendumps'
   endif
   call writefile([
 	\ 'set incsearch hlsearch scrolloff=0',
@@ -527,7 +527,7 @@ endfunc
 
 func Test_incsearch_with_change()
   if !has('timers') || !exists('+incsearch') || !CanRunVimInTerminal()
-    return
+    throw 'Skipped: cannot make screendumps and/or timers feature and/or incsearch option missing'
   endif
 
   call writefile([

src/nvim/testdir/test_startup_utf8.vim

@@ -63,7 +63,7 @@ endfunc
 
 func Test_detect_ambiwidth()
   if !CanRunVimInTerminal()
-    return
+    throw 'Skipped: cannot run Vim in a terminal window'
   endif
 
   " Use the title termcap entries to output the escape sequence.

src/nvim/testdir/test_syntax.vim

@@ -496,8 +496,8 @@ endfunc
 
 " Check highlighting for a small piece of C code with a screen dump.
 func Test_syntax_c()
-  if !has('terminal')
+  if !CanRunVimInTerminal()
-    return
+    throw 'Skipped: cannot make screendumps'
   endif
   call writefile([
 	\ '/* comment line at the top */',

src/nvim/testdir/test_tabpage.vim

@@ -558,7 +558,7 @@ endfunc
 
 func Test_tabpage_cmdheight()
   if !CanRunVimInTerminal()
-    throw 'Skipped: only works with terminal'
+    throw 'Skipped: cannot make screendumps'
   endif
   call writefile([
         \ 'set laststatus=2',