Customize: Remove use of reserved word `default` in Underscore template which breaks IE8.

Fixes regression introduced in [36769].

Merge of [37417] to the 4.5 branch.

Props adamsilverstein.
Fixes #36793.

Built from https://develop.svn.wordpress.org/branches/4.5@37450


git-svn-id: http://core.svn.wordpress.org/branches/4.5@37418 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/customize/class-wp-customize-media-control.php

@@ -214,7 +214,7 @@ class WP_Customize_Media_Control extends WP_Customize_Control {
 			</div>
 			<div class="actions">
 				<# if ( data.defaultAttachment ) { #>
-					<button type="button" class="button default-button">{{ data.button_labels.default }}</button>
+					<button type="button" class="button default-button">{{ data.button_labels['default'] }}</button>
 				<# } #>
 				<# if ( data.canUpload ) { #>
 				<button type="button" class="button upload-button" id="{{ data.settings['default'] }}-button">{{ data.button_labels.select }}</button>

wp-includes/version.php

@@ -4,7 +4,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '4.5.3-alpha-37445';
+$wp_version = '4.5.3-alpha-37450';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.