sv_upgrade from type 4 down to type 2

[Dave Mitchell]

Nick, looks like its easy to downgrade a scalar after all:

$ ./perl -we '$y="$x\n"; --$x'
Name "main::y" used only once: possible typo at -e line 1.
Use of uninitialized value $x in concatenation (.) or string at -e line 1.
sv_upgrade from type 4 down to type 2 at -e line 1.
$


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Please note that ash-trays are provided for the use of smokers,
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