Prevent data-uri function from embedding files larger than 32KB.

Although IE8 does support data-uris, it only does so with a limit of 32KB. It's a silly limitation, but a source of potential bugs. When the limit is exceeded, the data-uri() function will simply return a normal url() value with a relative path to the asset.

One may pass --no-ie-compat to lessc to avoid this safeguard.

test/browser/css/urls.css

@@ -44,3 +44,6 @@
   uri-1: url('http://localhost:8081/browser/less/../../data/page.html');
   uri-2: url('http://localhost:8081/browser/less/../../data/page.html');
 }
+#data-uri-toobig {
+  uri: url('http://localhost:8081/browser/less/../../data/data-uri-fail.png');
+}

test/browser/less/urls.less

@@ -43,3 +43,7 @@
   uri-1: data-uri('text/html', '../../data/page.html');
   uri-2: data-uri('../../data/page.html');
 }
+
+#data-uri-toobig {
+  uri: data-uri('../../data/data-uri-fail.png');
+}

test/css/urls.css

@@ -52,3 +52,6 @@
   uri-1: url('data:text/html,%3Ch1%3EThis%20page%20is%20100%25%20Awesome.%3C%2Fh1%3E%0A');
   uri-2: url('data:text/html,%3Ch1%3EThis%20page%20is%20100%25%20Awesome.%3C%2Fh1%3E%0A');
 }
+#data-uri-toobig {
+  uri: url(../data/data-uri-fail.png);
+}

test/less/urls.less

@@ -46,3 +46,8 @@
   uri-1: data-uri('text/html', '../data/page.html');
   uri-2: data-uri('../data/page.html');
 }
+
+// so, weirdly, the browser output is quoted, the less output is UNquoted
+#data-uri-toobig {
+  uri: data-uri('../data/data-uri-fail.png');
+}