ok jamsek

In preparation for wide sha256 support; stsp@ agrees. Change done mechanically with find . -iname \*.[cy] -exec sam {} + X ,x/<sha1\.h>/i/\n#include <sha2.h>

As reported by Jerome Kasper, got-index-pack would run out of memory while cloning projects like LLVM or the Linux kernel. The delta cache was pushed to its maximum size limit of ~2GB, which is much higher than the default user data limit on OpenBSD. Set the delta cache size limits to values which should result in the cache limiting itself to 128MB or less.

ok stsp

This approach uses more memory but is much faster. To offset the additional memory usage somewhat the cache now stores very small deltas only. However, overall memory usage goes up. Hopefully we will find a way to reduce this later. ok op@