Request context is unavailable during the Application_Start event of IIS7
integrated applications. The error "HttpException (0x80004005): Request is
not available in this context" will occur. To resolve the issue, we can
get the root path by using "HttpRuntime.AppDomainAppVirtualPath" instead.
Merge pull request #23 from LinkExe/IIS7CompatibilityUpdate

IIS7 Integrated Mode Compatibility Update