Closes #2309

Issue #2304

Closes #2200

Issue #2283

Issue #2282

Closes #2275

Closes #2274

Closes #2272

1) Fix a bug whereby multiple '\'es in the replace part of a search and replace
string were getting collapsed into a single one.
2) Split flipEscaping into two specialized functions -- one for the regex part,
and one for the replace part.

This produces saner widths for most elements, and removes
the need for the border/fit-width hack on the pre elements.

Issue #2256

Conflicts:
	lib/codemirror.js

Issue #2255

Also configure the htmlmixed option to pass through xml-mode-specific
options to its inner xml mode.

Issue #2265

(removed non-octave ... comments, added octave's # comments)

Closes #2268

Added a wrapper for js-yaml.js to enable YAML lint support. Followed
json-lint.js pattern. Unfortunately js-yaml.js only shows one error at
a time, but something is better nothing. Checked code with linter and
ran tests. All came back clean.

(Only works if anyword-hint.js is loaded.)

Doesn't take up any space now, so that a tab of width 2 is 2 em width
rather than 3.

Closes #2262

It apparently does not have a working buttons property on its mouse
events.

Issue #2260

The vim mode was making sensible use of a searchcursor with
a match-everything regexp as cursor.

Issue #2259

It doesn't do anything useful, and makes replace-all loop
forever.

Closes #2259

Issue #2256

... so that users can use \1, \2, etc in the replace expressions.