Add environment variable to create a full dump instead of a minidump
The Windows crash/freeze catcher currently creates a minidump, which only includes the stack, giving most of the information we might need in a small file. However, sometimes stuff on the heap can be useful, and creating a full dump with the heap would be good. That can be done by just passing one extra flag to the dump-creating Win32 function. This wouldn't be worthwhile most of the time, but fencing it off behind an environment variable would be viable.