Created Issue: Please make lessEngineConfig.DisableUrlRewriting configurable in web.config [22]

In the fix for issue #20 (commit 8292919a4254), you changed lessEngineConfig.DisableUrlRewriting = true; to lessEngineConfig.DisableUrlRewriting = false;

This in conjunction with the subsequent fix for #21 breaks our less in the following way:

```
@pageCurl: "/img/PageCurl.png";

header#header {
background: #fff url("@{pageCurl}") no-repeat right top;
}
```
renders as

```
header#header {
background: white url("/Content//img/PageCurl.png") no-repeat right top;
}
```

Can you have a setting in web.config that will allow us to enable or disable Url rewriting in .less files. Or just simply have the dotless interpreter use the existing dotless configuration from web.config. Or some other fix for this bug?

Thanks!