Try really hard to fix parallel installs. Add a bunch of .ORDER
directives to ensure that all realinstall sub-tasks are executed
after beforeinstall, similarly ensure that all afterinstall sub-
tasks are executed after realinstall. Demonstration:

all: task1 task2
.ORDER: task1 task2

task2: task2_subtask
.ORDER: task1 task2_subtask

task1 task2 task2_subtask:
@sleep jot -r 1 0 1.0
@echo ${.TARGET}

Without the second .ORDER directive, task2_subtask can be run in
parallel with task1.

Spotted by: Andrea Campi <andrea@webcom.it>