More hacks in character measurement to fix cursor at zero-width widget

Issue #1617
[themes] Fix unrestricted rules
[midnight theme] Remove some rules referring to classes CM does not use
[merge addon] Fix another layout issue
[rst] Emphasis and literal highlighting fix

Ensured that emphasis (weak & strong) plus literal syntax highlighting are rendered correctly even if the highlighted word is followed immediately by a non-word character (like an interpunction):

 * ```a word **strongly emphasised**?```;
 * ```a word *weakly emphasised*?```;
 * ```a word with ``literal emphasis``?```;

Further changed recognition order to `strong`, `weak`, `literal`, `number`, `positive`, `negative` and `link` to comply more with the reStructuredText spec (see http://docutils.sourceforge.net/docs/ref/rst/restructuredtext.html#recognition-order).
[rst] Reference name fix w.r.t. "phrase-references"

Phrase-references should be able to contain interpunction characters; fixed.
[smalltalk mode] add support for "#'...'" symbol syntax
[tern addon] Fix a few bugs
[tern addon] Pass file name and document to fileFilter
Add -moz-box-sizing rules to the styles that use box-sizing

Apparenly Firefox still hasn't caught up on the unprefixed version.
Propagate StringStream's match() fixes to runmode
[vim keymap] Define a vim option, register beforeSelectionChange handler

Issue #1084
Issue #1630
Fix bug in findWordAt

Which could result in a selection at a negative character offset
when double-clicking.

Issue #1638
[real-world uses] Add Fiddle Salad
[compression helper] Sort and complete addon scripts
[merge addon] Make sure synchronized scrolling scrolls other pane to top/bot
[merge addon] Synchronize vertical scrolling
[merge addon] Use CodeMirror-merge-* CSS class names

Since the addon is called merge, not diff.
[matchtags addon] Only highlight matching tag, try to be more efficient
Stabilize scroll position when removing widgets

(When they are above visible range, scroll up to correspond for
height reduction.)

Closes #1645