detect close failure on just-written file handles

I audited git for potential undetected write failures.
In the cases fixed below, the diagnostics I add mimic the diagnostics
used in surrounding code, even when that means not reporting
the precise strerror(errno) cause of the error.

Signed-off-by: Jim Meyering <jim@meyering.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin-init-db.c

@@ -40,7 +40,8 @@ static int copy_file(const char *dst, const char *src, int mode)
 		return fdo;
 	}
 	status = copy_fd(fdi, fdo);
-	close(fdo);
+	if (close(fdo) != 0)
+		return error("%s: write error: %s", dst, strerror(errno));
 
 	if (!status && adjust_shared_perm(dst))
 		return -1;