remove dual-valueness of v-strings (i.e., they are pure strings

remove dual-valueness of v-strings (i.e., they are pure strings
now); avoid the word "tuple" to describe strings represented as
character ordinals; usurp $PERL_VERSION for $^V as suggested by
Larry, deprecate $] ; adjust the documentation and testsuite
accordingly

p4raw-id: //depot/perl@5186