This commit takes care of a couple of things;

(a) a couple of typos in the source code

(b) adds a ctrl command and handling code to enable or disable the fork()
    checking that CHIL can do when applications are calling fork() in
    their application and using the library from multiple child processes
    after the one initialisation.

(c) adds another ctrl command to prevent the initialisation of the CHIL
    library from providing mutex-handling callbacks, even if the library
    has suitable callbacks already available. This can simplify (and
    optimise) applications that do not use multi-threading.