feat($compile): support tel: links in a[href]

Allow `tel:` links so that click-to-call works in mobile browsers

Author: benmccann

src/ng/compile.js

@@ -153,7 +153,7 @@ function $CompileProvider($provide) {
       Suffix = 'Directive',
       COMMENT_DIRECTIVE_REGEXP = /^\s*directive\:\s*([\d\w\-_]+)\s+(.*)$/,
       CLASS_DIRECTIVE_REGEXP = /(([\d\w\-_]+)(?:\:([^;]+))?;?)/,
-      aHrefSanitizationWhitelist = /^\s*(https?|ftp|mailto|file):/,
+      aHrefSanitizationWhitelist = /^\s*(https?|ftp|mailto|tel|file):/,
       imgSrcSanitizationWhitelist = /^\s*(https?|ftp|file):|data:image\//;
 
   // Ref: http://developers.whatwg.org/webappapis.html#event-handler-idl-attributes