Capsicumize bspatch

Move all of the fopen() and open() calls to the top of main()

Restrict each FD to least privilege (read/seek only, write only, etc)

cap_enter(), and make all except the output FD read/seek only.

Reviewed by: emaste, ed, oshogbo, delphij
Approved by: so
MFC after: 3 days
Relnotes: yes
Sponsored by: ScaleEngine Inc.
Differential Revision: https://reviews.freebsd.org/D7358