Use filename recorded in position

Author: andreypopp

lib/compiler.js

@@ -46,7 +46,7 @@ Compiler.prototype.emit = function(str, pos, startOnly) {
         line: this.position.line,
         column: Math.max(this.position.column - 1, 0)
       },
-      source: 'source.css',
+      source: pos.source || 'source.css',
       original: {
         line: pos.end.line,
         column: pos.end.column - 1