kes All code added back. Fixed block.c read/write to loop only 3

kes  All code added back. Fixed block.c read/write to loop only 3
     times. This apparently keeps the OS from crashing (at least
     most of the time).
kes  The kernel bug still persists. Backup something then immediately
     do a bscan on the same tape, and the kernel will crash.
kes  Simplifed tape open().  It no longer uses nonblocking mode, which
     means that opening with no tape loaded will probably take at least
     6 minutes before an error is reported.
kes  Do not use MTSETDRVBUFFER if not running as root.  Do a MTRESET
     when doing set_os_device_parameters.
kes  Report open error in mount.c
kes  Remove all .exe files from the installer directory on make clean.