ed: simplify edInsert() (#550)

* Rewrite edInsert() without @tmplines2 and $tmp_chars
* Use splice() to add @tmp_lines into @lines directly
* Use scalar(@tmp_lines) instead of $tmp_chars to indicate whether @lines needs to be updated (early return added)
* Input address normally counts from 1 so handles the placeholder at $lines[0]
* Input address 0 is allowed for 'a' and 'i' commands, so be careful not to move $lines[0] placeholder
* In edEdit() be more careful to reset @lines if no file is being read; the array needs to have one element
* test1: start ed on empty buffer and run '0i' or '0a', enter text terminated with '.' line
* test2: start ed with text file with 9 lines and run '9a'; text is appended starting from line 10
* test3: apply an ed patch containing 'a' commands (below)

%perl diff -e ed.new ed > patch.ed
%echo w >> patch.ed 
%perl ed ed.new < patch.ed 
30368
29383
%perl sum -a md5 ed ed.new 
e5748aef0ba835feb1daba4a99778b9c  ed
e5748aef0ba835feb1daba4a99778b9c  ed.new

bin/ed

@@ -693,6 +693,7 @@ sub edEdit {
         $filename = $RememberedFilename;
     } else {
         $CurrentLineNum = 0;
+        @lines = (0);
         return 1;
     }
 
@@ -761,7 +762,7 @@ sub edEdit {
 
 sub edInsert {
     my($Mode) = @_;
-    my(@tmp_lines,@tmp_lines2,$tmp_chars);
+    my(@tmp_lines);
 
     if (defined($adrs[1])) {
         edWarn(E_ADDREXT);
@@ -776,31 +777,22 @@ sub edInsert {
     }
 
     # suck the text into a temp array
-
-    @tmp_lines = ();
-    $tmp_chars = 0;
-
     while (<>) {
         last if (/^\.$/);
         push(@tmp_lines,$_);
-        $tmp_chars += length;
+    }
+    if (scalar(@tmp_lines) == 0) {
+        return 1;
     }
 
     my $src = $adrs[0];
-    $src-- if ($src && $Mode == $INSERT_MODE);
+    $src++ if ($src && $Mode == $APPEND_MODE);
+    $src++ if $src == 0; # 0a == 0i == 1i
 
-    shift @lines; # get rid of 0 line
-    @tmp_lines2 = splice @lines, 0, $src;
-    unshift @lines, @tmp_lines;
-    unshift @lines, @tmp_lines2;
-    $CurrentLineNum = $src + scalar(@tmp_lines);
-    unshift @lines, undef; # put 0 line back
-
-    if ($tmp_chars) {
-        $NeedToSave = 1;
-        $UserHasBeenWarned = 0;
-    }
+    splice @lines, $src, 0, @tmp_lines;
 
+    $NeedToSave = 1;
+    $UserHasBeenWarned = 0;
     return 1;
 }