Only style :hover state for :enabled buttons

Signed-off-by: Alex Coles <alex@alexbcoles.com>

app/assets/stylesheets/global/_mixins.sass

@@ -113,7 +113,7 @@ $button_gray_font_color: #222222
   background: $button_highlight_background_gradient_ms
   background: $button_highlight_background_gradient
 
-  &:hover
+  &:enabled:hover
     border: 1px solid $button_highlight_background_hover_color
     background: $button_highlight_border_hover_color
 
@@ -127,7 +127,7 @@ $button_gray_font_color: #222222
   background: -ms-linear-gradient(top,  #ffffff 0%,#eeeeee 74%,#eeeeee 100%)
   background: linear-gradient(to bottom,  #ffffff 0%,#eeeeee 74%,#eeeeee 100%)
 
-  &:hover
+  &:enabled:hover
     border: 1px solid #777777
     background: -moz-linear-gradient(top,  #ffffff 0%, #eeeeee 40%, #ddd 100%)
     background: -webkit-gradient(linear, left top, left bottom, color-stop(0%,#ffffff), color-stop(40%,#eeeeee), color-stop(100%,#ddd))