Add xbuild tools from the new native-xbuild target in head.  This creates an amd64/i386 binary toolchain to output arm or mips binaries.  Runs without full emulation and speeds up cross builds
Remove the redirection for MAKE.  It appears that we do not know how to assemble bmake in a way that is useable.  breaks shells/bash
Remove arguments to check_emulation calls as uneeded.
Add notes in jail section about what the -x argument is used for.

Noted by bdrewery.
Now that kern_exec.c has been modified to be able to handle multiple image activators, go ahead and enable MAKE again.
Fix mdoc
Update ZSH completions
Merge branch 'origin/pr/19' into release-3.1

* origin/pr/19:
  Update ZSH completions
  Fix mdoc
  Now that kern_exec.c has been modified to be able to handle multiple image activators, go ahead and enable MAKE again.
  Add notes in jail section about what the -x argument is used for.
  Remove arguments to check_emulation calls as uneeded.
  Remove the redirection for MAKE.  It appears that we do not know how to assemble bmake in a way that is useable.  breaks shells/bash
  Add xbuild tools from the new native-xbuild target in head.  This creates an amd64/i386 binary toolchain to output arm or mips binaries.  Runs without full emulation and speeds up cross builds

Merged from https://github.com/bdrewery/poudriere_old/pull/19