Flush PL_stashcache when assigning a file handle to a typeglob.

Flush PL_stashcache when assigning a file handle to a typeglob.

File handles take priority over stashes for method dispatch. Assigning a
file handle to a typeglob potentially creates a file handle where one did
not exist before. As PL_stashcache only contains entries for names which
unambiguously resolve to stashes, such a change may mean that PL_stashcache
now contains an invalid entry. As it's hard to work out exactly which entries
might be affected, simply flush the entire cache and let it rebuild itself.