ngChange not available for md-input and md-text-float

[fabiancook]

No description provided.

[Frank3K]

Related: #523

[ajoslin]

#547

[jamesjnadeau]

I was able to use the following successfully to work around md-text-float not having direct support for ngChange

<md-input-group>
    <label for="spell_word">Spell Word</label>
    <md-input id="spell_word"
        ng-model="word_guess" ng-change="check_spelling()">
    </md-input>
</md-input-group>

check_spelling() is being correctly called now.

Epiphany came about when I was trying to add in ngChange handling to md-text-float.