[v3] hashtable fw decl fix

[Benjamin De Kosnik]

This patchlette needed for versioned builds, just makes
declaration/foward declaration consistent.

-benjamin

tested x86/linux
tested x86/linux versioned namespaces
-------------- next part --------------
A non-text attachment was scrubbed...
Name: 20120501-1.patch
Type: text/x-patch
Size: 659 bytes
Desc: not available
URL: <http://gcc.gnu.org/pipermail/libstdc++/attachments/20120502/c31f3414/attachment.bin>