jquery: Make code-listing line numbers unselectable

Prevent accidental inclusion of the line numbers
when copy-pasting from syntax highlighter code blocks
via `user-select: none`.

Also use `-webkit-user-select` for Safari (desktop & mobile)
and `-ms-user-select` for IE.

Closes gh-436

Signed-off-by: FeRD (Frank Dana) <ferdnyc@gmail.com>

Author: ferdnyc

themes/jquery/css/base.css

@@ -3793,6 +3793,9 @@ pre .diff .hljs-comment {
 .syntaxhighlighter table td.gutter .line {
 	text-align: right !important;
 	padding: 0 0.5em 0 1em !important;
+	-webkit-user-select: none;
+	-ms-user-select: none;
+	user-select: none;
 }
 .syntaxhighlighter table td.code .line {
 	padding: 0 0.5em !important;