CXMAN-14: Use "file" to verify image types
CXMAN-14: Use "file" to verify image types

We used to do this anyway, but I removed it for windows support.
Of course, Cygwin has the "file" tool anyway so we should be ok.

Cynerva/cxmanage,SLS-Dev/cxmanage,SilverLiningSystems/cxmanage-test,SilverLiningSystems/cxmanage-test2,Cynerva/cxmanage,SilverLiningSystems/cxmanage-test2,SilverLiningSystems/cxmanage-test,SLS-Dev/cxmanage