toke.c: Stop using len to indicate trailing ::

This variable stores the length of the word we are parsing.  But at
one point it starts being used as a boolean to indicate that we have a
bareword ending in two colons.  So if are looking up are bareword that
does not end in ::, we have to call strlen() to scan the string and
determine the length.
MAD leftovers in toke.c
Don’t call intuit_method twice for the same barewords

This calls intuit_method once:

    sub fooo; print foo bar

This calls it twice:

    sub foo; print foo bar

because seeing whether we are dealing with a bareword after ‘print’,
‘say’ etc. must happen *before* we look past the space after ‘foo’ to
see whether ‘foo bar’ could be a method call.  That’s because skipping
a space could reset the internal variables that track whether we have
just seen ‘print’.

Hence, we end up with a call to intuit_method (i.e., is this a
method?) inside the block that deals with print FOO.

But then we have another call to intuit_method later that deals with
the non-print cases.

But the former can fall through to the latter if we don’t have a
method call here.  And then intuit_method is called again with exactly
the same arguments.  So we just repeat the check needlessly.

Avoiding the call the second time (if we have already called it above)
will allow the next commit to put a GV lookup that occurs only for the
sake of intuit_method directly inside intuit_method, avoiding the need
for that lookup for most barewords.
Avoid duplicate GV lookup for barewords

Since commit f74617600 (5.12), the GV lookup that this commit removes
from yylex has only been used to see whether the bareword could be a
filehandle.  The result is used by intuit_method to decide whether we
have a method call for ‘foo bar’ or ‘foo $bar’.

Doing this lookup for every bareword we encounter even when we are not
going to call intuit_method is wasteful.

The previous commit ensured that intuit_method is called only once
for each bareword, so we can put that gv lookup directly inside
intuit_method.