There's a typo in r183242 which causes jexec to be also skipped:
--- head/usr.sbin/Makefile 2008/09/19 19:20:05 183195
+++ head/usr.sbin/Makefile 2008/09/21 22:02:26 183242
<...>
+.if ${MK_JAIL} != "no"
+_jail= jail
+_jexect= jexec
+_jls= jls
+.endif
Marius