Fix #58 fix #59

If a user sets cache as "/", this gets converted to "C:\cygwin64". Instead of
coverting back to "/", causing an error with "mkdir", we can just use
"C:\cygwin64" as is. "DosFileWarning" now off by default, so it should not be
necessary to convert cache path to Unix form.

http://cygwin.com/ml/cygwin/2015-07/msg00432.html

apt-cyg

@@ -132,7 +132,7 @@ function find-workspace {
     getline
     print $1
   }
-  ' /etc/setup/setup.rc | cygpath -f-)
+  ' /etc/setup/setup.rc)
 
   mirror=$(awk '
   /last-mirror/ {