Fix bug where backslashes in inline diffs could be dropped

This MR fixes a bug in inline diff generation causing backslashes to be dropped. For example, the input:

input.to_s.sub(/[\r\n].+/,'').sub(/\\[rn].+/, '').strip

The second backslash is dropped in the second sub statement:

With this fix, it looks like:

Closes #2253 (closed)

Hah. This exposes another bug, where the actual diff has:

"-    input.#!idiff-start!##!idiff-finish!#sub(/[\\r\\n].+/,'').sub(/\\\\[rn].+/, '').strip\n",
"+    input.#!idiff-start!#to_s.#!idiff-finish!#sub(/[\\r\\n].+/,'').sub(/\\\\[rn].+/, '').strip\n",

But it is rendered as:

Reassigned to @DouweM

Status changed to merged

mentioned in commit c9920c42