Integrate changes #9137,9138,9142 from maintperl into mainline.

Integrate changes #9137,9138,9142 from maintperl into mainline.

fix leak in pregcomp() when RE fails to compile (e.g. m/\\/)

remove squelch controls for "Scalars leaked" messages in most places
(these are now cured)

fix another memory leak reported by purify (tie callbacks that
croak can leak when wiping out magic)

p4raw-link: @9142 on //depot/maint-5.6/perl: 26972843796e21c404c9d13ec5ee86e7b952a2bd
p4raw-link: @9138 on //depot/maint-5.6/perl: ad7f1144250940f9ca43bac32708ec5e718b30ff
p4raw-link: @9137 on //depot/maint-5.6/perl: 1f35595ecca168b4f66e3399344799fdbd496d17

p4raw-id: //depot/perl@9144
p4raw-integrated: from //depot/maint-5.6/perl@9143 'copy in'
	t/pragma/strict-vars (@7318..) t/pragma/warn/regcomp (@7887..)
	t/op/regexp.t (@8551..) t/op/lex_assign.t (@8987..) 'merge in'
	t/op/local.t (@5902..) t/pragma/warn/op (@7846..)
	t/pragma/warnings.t (@7895..) t/comp/proto.t (@8173..)
	t/pragma/warn/toke (@8570..) regcomp.c (@8777..) scope.c
	(@8855..) t/op/pat.t (@9076..)