ed: simplify edInsert()

[mknos]

• 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