Unquote spawned command verbs on VMS.

Unquote spawned command verbs on VMS.

Prior to the current change,

$ foo "A" "b" "c"

worked, but the following didn't:

$ "foo" "A" "b" "c"
%DCL-E-PARSEFAIL, error parsing DCL$PATH:"foo".*
-RMS-F-FNM, error in file name

even if foo was a valid command or path.  It's illegal in DCL to
quote the command verb even if it's often necessary to quote the
parameters to it.

But various things in the wild (such as Test::Harness::_filtered_inc),
find it convenient or necessary to quote the command verb, so the
easiest way to support that is to unquote it before DCL sees it, and
that's what this change does.

Also, spaces within the first quoted item are now escaped so that
an image path containing spaces doesn't run afoul of subsequent
tokenizing based on spaces.