[misc] Print console warning when setting non-existent locales

[asulaiman]

Right now if the new locale being set is not available then it fails silently and just uses the existing global locale. A console warning would be useful to notify the user of such a failure.

[ichernev]

@asulaiman if you want to use console.warn you should do it extremely carefully like here :

moment/src/lib/utils/deprecate.js

Line 7 in 497f918

(typeof console !== 'undefined') && console.warn) {

[asulaiman]

@ichernev Ive added the console warn checks. Not sure if they are really needed because console console.warn are fairly big dependencies in JS that i dont see going away but i get it that we should be doing this regardless for consistency.

[ichernev]

@asulaiman you're also missing a space after key.