[ticket/15424] Multiple typo fixes in docs & comments

Fixed typos in some docs, guidelines, some non-user-facing files.

PHPBB3-15424

phpBB/styles/prosilver/template/forum_fn.js

@@ -460,7 +460,7 @@ function parseDocument($container) {
 			$linksLast = $linksNotSkip.filter(filterLast), // The items that will be hidden last
 			persistent = $this.attr('id') === 'nav-main', // Does this list already have a menu (such as quick-links)?
 			html = '<li class="responsive-menu hidden"><a href="javascript:void(0);" class="js-responsive-menu-link responsive-menu-link"><i class="icon fa-bars fa-fw" aria-hidden="true"></i></a><div class="dropdown"><div class="pointer"><div class="pointer-inner" /></div><ul class="dropdown-contents" /></div></li>',
-			slack = 3; // Vertical slack space (in pixels). Determines how sensitive the script is in determining whether a line-break has occured.
+			slack = 3; // Vertical slack space (in pixels). Determines how sensitive the script is in determining whether a line-break has occurred.
 
 		// Add a hidden drop-down menu to each links list (except those that already have one)
 		if (!persistent) {

phpBB/styles/prosilver/theme/icons.css

@@ -5,7 +5,7 @@
 /* Global module setup
 --------------------------------*/
 
-/* Renamed version of .fa class for agnostic useage of icon fonts.
+/* Renamed version of .fa class for agnostic usage of icon fonts.
  * Just change the name of the font after the 14/1 to the name of
  * the font you wish to use.
  */

phpBB/styles/prosilver/theme/print.css

@@ -90,7 +90,7 @@ hr {
 	font-size: 75%;
 }
 
-/* Dont want to print url for names or titles in content area */
+/* Don't want to print url for names or titles in content area */
 .postbody .author a:link, .postbody .author a:visited,
 html>body .postbody .author a:link:after,
 html>body .postbody .author a:visited:after,