key/value hash slice operation

kvhslice operator that implements %h{1,2,3,4} syntax which
returns list of key value pairs rather than just values
(regular slices).
scalar value %x{'a'} better written as $x{'a'}
index/value array slice operation

kvaslice operator that imlements %a[0,2,4] syntax which
result in list of index/value pairs. Implemented in
consistency with "key/value hash slice" operator.
test key/value hash slices
test index/value array slices
short documentation for key/value hash/array slices
update manifest
Suppress a warning in kvhslice.t

The bugginess of the ‘Scalar value better written as...’ warning
applies to %new{silce} syntax, too.
Hard-code op name in ck_exists|delete errors

The reason is manifold:
• ck_exists and ck_delete are each only ever called with one op type,
  so we can hard-code the op, which takes less code.
• The messages in perldiag are more helpful if they include
  the op name.
• Changing them in op.c too avoids the need for
  diag_listed_as clutter.

(I know, two of these are not listed in perldiag yet.  I’m get-
ting to that.)
Add two missing perldiag entries
Use diag_listed_as two suppress two diag.t failures
Sort MANIFEST
Add new opcodes to Opcode.pm
Increase $Opcode::VERSION to 1.26
Increase $B::Deparse::VERSION to 1.23
pp.c:pp_kvhslice: remove unused var
perldata.pod: consistent spaces after dots
perldata.pod: Capitalise =head3 consistently
Improve new slice docs in perldata.pod
pp.c: Allow 64-bit stack offsets in kv[ah]slice