45-shell.t: fix duplicate load of AngelPS1::Shell::mksh
70-examples.t: simplify, by using globs
mksh: bring the implementation similar to POSIX

... for incoming refactor to make it @ISA !
POSIX: extract the 'local' shell keyword

... to make it overridable in sub classes.
For example, ksh93 doesn't have it and uses 'typeset' instead.
ksh93's @ISA becomes POSIX

ksh93 now inherits from POSIX instead of mksh.
mksh now inherits from POSIX

The shell_code_dynamic was almost the same. It is now shared with
inheritance.