Reorder t/lib/croak/toke

to put string terminator errors all in one place.
toke.c: Add comment for greppability
Correct ‘"my" variable "&f::b"...’ message

"my" variable &foo::bar can't be in a package at - line 2, near "my sub foo::bar"

It should say ‘subroutine’, not ‘variable’.  When I implemented lexi-
cal subs, I thought I caught all these, must I missed this one.
Deparse-core.t: Fix ineffective tests

In a958cfbb8, I accidentally changed this to test ‘test::foo()’,
rather than ‘foo()’ deparsing as ‘test::foo()’, which was what I
had intended.
Deparse with CORE:: to avoid lex sub conflicts

If a lexical sub with the same name as a keyword is in scope, we need
to deparse the keyword with a CORE:: prefix.

This commit handles most of the cases, but there are a few exceptional
cases remaining.