sysutils/copytape: include errno.h for errno

errno must be accessed by a macro from errno.h.

Tidy includes and add unistd.h for read/write.

Consolidate patches for easy of maintenance.

This code is borderline useless and certainly broken with modern tape
sizes due to the use of ints for sizes.

PR: 281781
Approved by: sjroz@verizon.net (maintainer)