Installer fixes

Get mkspecs right (not everyone has the same user name as me).
Get headers right (before it only installed the forwarding headers).
Show windows style paths in installer (c:\... instead of c:/...).
Allow spaces in target dir.
Make it possible to build installer on linux
Merge pull request #181 from gladhorn/installer

Installer fixes
Merge pull request #185 from nierob/master

Small improvements
Fix EnginioModel behaivour when an cached object was removd externally.