add boolean context support to several ops

For some ops which return integer values and which have a reasonable
likelihood of being used in a boolean context, set the OPpTRUEBOOL
flag on the op as appropriate, and at runtime return &PL_sv_yes /
&PL_sv_zero rather than an integer value.

This is especially beneficial where the op doesn't have a targ, so has
to create a mortal SV to return the integer value.

Similarly, its a win where it may be expensive to calculate an integer
return value, such as pos() or length() converting between byte and char
offset.

Ops done:

    OP_SUBST
    OP_AASSIGN
    OP_POS
    OP_LENGTH
    OP_GREPWHILE

0 files changed, 0 insertions, 0 deletions