5.1.1

This is mostly a bugfix release. There is one major new
feature: the Boutiques integrator now has hooks to
allow a superclass to override its subclasses behavior (!),
which is useful when coding special integrators. The
current use case is the BidsAppHandler class in the
cbrain-plugins-neuro package.

Bugs fixed:

• Spawned subprocesses woudl no longer log exceptions and just
  disappear; handler code was still using the old Mysql::Error
  instead of Mysql2::Error
• Bourreaux now set the env variable OBJC_DISABLE_INITIALIZE_FORK_SAFETY=yes
  this is needed on latest maxOS versions
• User messages are properly appended to 'read' messages
• Tool forms are adjusted slightly
• The boot process now lists each task descriptor has it is being integrated
• Some better docs