Using a variable for ng-show-auth would fail
Using a variable for ng-show-auth would fail

ng-show-auth was always expecting the value to be a string, this causes
problems if you want to dynamically build some items using, say, an ng-repeat.
Replaced the compile with a link (saw no explicit reason for the compile over
link in this function) and attempt to evaluate the value of the ng-show-auth
attribute. If this evaluates to undefined, we fall back to just using it as a
string, thus not breaking previous code using this method.

Alternatively a breaking change could be done by not allowing the fallback, but
instead requiring explicit strings as the attribute, such as:
`<a href="#/secret" ng-show-auth="'login'">Not For Your Eyes</a>`

joehannes-generation/angularfire-seed,morganric/wildfirio,ap149/angularfire-seed,deuxnids/ruhrig,clarkdever/ITNShadow,JonBergman/angularfire-seed,u910328/Coding-Parrot-2.1,russellf9/f9-angular-fire,JonBergman/angularfire-seed,dialectica/angularfire-testbed,timothy-clifford/dashshelf,missmellyg85/books,rawrsome/angularfire-seed,pmconnolly80/angularfire-seed,birdwell/FantasyFootball,rawrsome/angularfire-seed,pmconnolly80/angularfire-seed,birdwell/Fantasy-Football,semiosis/moop-mapp,snowpeame/snowpeas,ap149/angularfire-seed,kmarwah/Seed,stevewitman/angularfire-seed,missmellyg85/angularfire-seed,joehannes-generation/angularfire-seed,kellsbells/freezing-octo-dubstep,bthj/like-breeding,russellf9/diary,stevewitman/angularfire-seed,baolocdo/angularfire-seed,semiosis/moop-mapp,morganric/wildfirio,quantiply-fork/angularfire-seed,snowpeame/snowpeas,harish-myaccount/vigilante,FirstBuild/InventoryMgmt-GroceryList,kmarwah/Seed,googlearchive/angularfire-seed,missmellyg85/books,clarkdever/ITNShadow,timothy-clifford/dashshelf,dialectica/angularfire-testbed,harish-myaccount/vigilante,missmellyg85/angularfire-seed,birdwell/FantasyFootball,u910328/Coding-Parrot-2.1,baolocdo/angularfire-seed,googlearchive/angularfire-seed,henry-hz/angularfire-seed,hoeghen/Login_template,robotnoises/angularfire-seed,birdwell/Fantasy-Football,robotnoises/angularfire-seed