fixes #3706: add textColor and textShadow as options to .buttonBackground mixin

less/buttons.less

@@ -15,12 +15,10 @@
   font-size: 13px;
   line-height: 20px;
   *line-height: 20px;
-  color: @grayDark;
   text-align: center;
-  text-shadow: 0 1px 1px rgba(255,255,255,.75);
   vertical-align: middle;
   cursor: pointer;
-  .buttonBackground(@btnBackground, @btnBackgroundHighlight);
+  .buttonBackground(@btnBackground, @btnBackgroundHighlight, @grayDark, 0 1px 1px rgba(255,255,255,.75));
   border: 1px solid @btnBorder;
   *border: 0; // Remove the border to prevent IE7's black border on input:focus
   border-bottom-color: darken(@btnBorder, 10%);
@@ -105,23 +103,6 @@
 // Alternate buttons
 // --------------------------------------------------
 
-// Set text color
-// -------------------------
-.btn-primary,
-.btn-primary:hover,
-.btn-warning,
-.btn-warning:hover,
-.btn-danger,
-.btn-danger:hover,
-.btn-success,
-.btn-success:hover,
-.btn-info,
-.btn-info:hover,
-.btn-inverse,
-.btn-inverse:hover {
-  color: @white;
-  text-shadow: 0 -1px 0 rgba(0,0,0,.25);
-}
 // Provide *some* extra contrast for those who can get it
 .btn-primary.active,
 .btn-warning.active,