fixes send.sh test fallout on arm64 and should also fix i386 ok op@

ok op

This adds a set of functions to abstract over SHA1Init, SHA1Update, SHA1Final, their respective SHA256 variants and how to compare digests. Replace all the SHA1*() usage with the new APIs. It's a preparatory step for sha256 handling. ok stsp@

Don't rely on AC_RUN_IFELSE as this breaks cross-compilation (voidlinux). Although this is better replaced with AC_CHECK_DECL. In template/ include checking for libbsd.

This is included portably.

Simply the SHA detection by not predicating on libcrypto, but instead checking individual header files.

Remove sha1.h as this is found portably across systems.

sha1.c -> hash.c

it abstracts over the hash type and ensures that object ids are zero'ed before their sha1 digest is written. Needed by the incoming sha256 support. ok stsp@

It will soon grow functions to deal with sha256 too. stsp@ agrees.

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>

Patch by Josiah Frentsos, thanks!

Don't assume commit info is always written. This is only true when diffing a commit against (one of) its direct parent(s). Otherwise we perform an invalid read on a tmp got_diff_line array and end up passing bogus offsets to fseeko(). Bug found and fixed by stsp with a minor tweak by me. ok jamsek for stsp's initial diff ok stsp@

This fixes the (harmless) errors raised by gitconfig.c on indented comment lines and adds a test case for it. Reported by James Cook, thanks! ok stsp@

The first example is meant to show the default values for all the options. Sync with reality.