If the submodule config is already in memory, and we can’t find the
desired name in there, check back on disk for it. This is especially
important when diffing, since it’s possible that further changes could
have occurred since the configuration was reloaded.

Check for EWOULDBLOCK as well as EAGAIN on write.

On some systems, notably HP PA-RISC systems running Linux or HP-UX,
EWOULDBLOCK and EAGAIN are not the same value.  POSIX (and these OSes) allow
EWOULDBLOCK to occur on write(2) (and send(2), etc.), so check explicitly
for this case as well as EAGAIN by defining and using a macro GIT_ISBLOCKED
that considers both.

The macro is necessary because MSYS does not provide EWOULDBLOCK and
compilation fails if an attempt is made to use it unconditionally.  On most
systems, where the two values are the same, the compiler will simply
optimize this check out and it will have no effect.

Fix filter test for CRLF->LF issues

Never convert CRLF->LF

Core git performs no conversion on systems that use LF, emulate that.

Handle `core.autocrlf=input` when checking out

Conditional ref update fixups

Keep the reflog parameters as the last two, as they're the optional
parameters.