FAKE typeglobs seriously busted (with patch)

FAKE typeglobs seriously busted (with patch)

Handling of fake typeglobs (scalars that are really globs
in disguise) is seriously busted since 5.002 (it wasn't
so in 5.001n).
The problem is that mg_get() on a glob calls gv_efullname()
which might coerce its first arg to a string.

Sub-critical patch to conceivably fix some %SIG problems. (Shared hash key
weren't being properly detected by some of the sig magic, but as shared
hash keys wouldn't normally be used in %SIG it's unlikely this is a
significant problem.)

This patch changes neither behavior nor performance.  However, it does
reduce code size and improve maintainability by combining some common
code in gv_fullname() and gv_efullname().