Add the ability to create CSS sprites and have them generated at compile time

1. Start a new MVC project with VS2012.
2. Install the following nugets:
   a) Twitter.Bootstrap.Less
   b)Frappe.MSBuild
3. Add a new bundle that just references ..\Content\bootstrap\bootstrap.less
4. Compile. Note that the generated bundle is empty.
5. Change the bundle to reference the file ..\Content\bootstrap\normalize.less
6. Note that the generated css file is compiled

From what I see, it looks like it SHOULD work. If it's breaking on something in the less files, it's not telling me where it's having an issue. I have verbosity turned on in the Output.

If you have a Less file with multiple nested imports, this can cause an issue where when one of them is updated the output of the bunlde is not updated as well. It only happens when everything is up-to-date except for the nested import.

If you have a @import statement in Less or Css which causes a recursive import, Frappe will crash msbuild.

Issue

Steps to Repo

1. Build the web app
2. Change a bundle
3. Build the web app, again

Expected Behavior

The bundle output should have been updated.

Experienced Behavior

The bundle output wasn't updated.

Known Workarounds

1. Rebuild the web app

OR

1. Run msbuild to build the site

Issue

The below is the output of the Package Manager Console when you update the Frappe.Mvc4 package.

Updating 'Frappe.Mvc4' from version '1.1.0.0' to '1.2.0.0' in project 'Frappe.Web.Mvc4.Razor.Example'.
Successfully removed 'Frappe.Mvc4 1.1.0.0' from Frappe.Web.Mvc4.Razor.Example.
Successfully removed 'Frappe.MSBuild 1.1.0.0' from Frappe.Web.Mvc4.Razor.Example.
Successfully installed 'Frappe.MSBuild 1.2.0.0'.
Successfully added 'Frappe.MSBuild 1.2.0.0' to Frappe.Web.Mvc4.Razor.Example.
Successfully installed 'Frappe.Mvc4 1.2.0.0'.
Successfully added 'Frappe.Mvc4 1.2.0.0' to Frappe.Web.Mvc4.Razor.Example.
Successfully uninstalled 'Frappe.Mvc4 1.1.0.0'.
Access to the path 'C:\Users\radleta\Dropbox\GitHub\Frappe\Examples\packages\Frappe.MSBuild.1.1.0.0\tools\Frappe.dll' is denied.
Access to the path 'C:\Users\radleta\Dropbox\GitHub\Frappe\Examples\packages\Frappe.MSBuild.1.1.0.0\tools\Frappe.MSBuild.dll' is denied.
Access to the path 'C:\Users\radleta\Dropbox\GitHub\Frappe\Examples\packages\Frappe.MSBuild.1.1.0.0\tools\Frappe.dll' is denied.
Access to the path 'C:\Users\radleta\Dropbox\GitHub\Frappe\Examples\packages\Frappe.MSBuild.1.1.0.0\tools\Frappe.MSBuild.dll' is denied.
Access to the path 'C:\Users\radleta\Dropbox\GitHub\Frappe\Examples\packages\Frappe.MSBuild.1.1.0.0\tools\Frappe.dll' is denied.
Access to the path 'C:\Users\radleta\Dropbox\GitHub\Frappe\Examples\packages\Frappe.MSBuild.1.1.0.0\tools\Frappe.MSBuild.dll' is denied.
The directory is not empty.

Successfully uninstalled 'Frappe.MSBuild 1.1.0.0'.

It appears MSBuild.exe still has locks on the files.

Known Workarounds

It just leaves legacy files. You can manually clean it up.

1. Close Visual Studio
2. Kill all MSBuild.exe processes
3. Delete the packages\Frappe.MSBuild* directory

If you comment out a @import statement in Less or Css, it's still looked at by Frappe.

The bundle output looked at the children last access date instead of the last write date. This would cause the bundle output to not be updated when the modify date changed without the last access date changing.