doc: remove executable bits from Changes, Makefile.PL and README

As Kent Fredric mentioned in RT#113625, Changes and README have erroneous
wise -x bit set. Being bit more strict, Makefile.PL shouldn't executed
directly but using

  perl Makefile.PL

to have the right perl used. Tricky #!perl lines aren't 100% supported
by all shells etc., neither is env always places in /usr/bin - so treat
all similar, force picking the right $^X.

Signed-off-by: Jens Rehsack <[email protected]>

Author: rehsack