Not sure if this is wanted, and it obviously has some knock on effects 
on package and snapshot generation.

But, cygport names detached debug info files by appending the .dbg 
suffix.  This is 'obviously correct' as it means that both a foo.exe and 
foo.dll can exist and have detached debug info.

For consistency, the attached patch changes the name of the detached 
debug info file for cygwin1.dll from cygwin1.dbg to cygwin1.dll.dbg