Make sure that mixed case alpha filters are handled correctly in IE. Fixes #5632.

src/css.js

 (function( jQuery ) {
 
-var ralpha = /alpha\([^)]*\)/,
+var ralpha = /alpha\([^)]*\)/i,
 	ropacity = /opacity=([^)]*)/,
 	rdashAlpha = /-([a-z])/ig,
 	rupper = /([A-Z])/g,

test/unit/css.js

@@ -112,7 +112,7 @@ if(jQuery.browser.msie) {
 		jQuery('#foo').css("filter", "progid:DXImageTransform.Microsoft.Chroma(color='red');");
   	equals( jQuery('#foo').css('opacity'), '1', "Assert opacity is 1 when a different filter is set in IE, #1438" );
 
-    var filterVal = "progid:DXImageTransform.Microsoft.alpha(opacity=30) progid:DXImageTransform.Microsoft.Blur(pixelradius=5)";
+    var filterVal = "progid:DXImageTransform.Microsoft.Alpha(opacity=30) progid:DXImageTransform.Microsoft.Blur(pixelradius=5)";
     var filterVal2 = "progid:DXImageTransform.Microsoft.alpha(opacity=100) progid:DXImageTransform.Microsoft.Blur(pixelradius=5)";
     jQuery('#foo').css("filter", filterVal);
     equals( jQuery('#foo').css("filter"), filterVal, "css('filter', val) works" );