Compile dtksh on FreeBSD

Compile dtksh on FreeBSD

dtksh can be now compiled on FreeBSD. Work in progress.

Needs a real Korn shell to bootstrap as $(KSHELL).
KSHELL is set by default to /usr/local/bin/ksh93
(generic POSIX shell may not work)

Tested on:

  FreeBSD 9.0-BETA1 #0 r224912M amd64

Known issues:

xvmstat:
* sleep does not work well (SIGSTOP is delivered)
xpong:
* xpong: line 220:  ball1x = max_x * 2.2 / 3 : arithmetic syntax error
* dtksh is rebuilt uncondtionally every time make is invoked