[PATCH] Safely store user locks in threads::shared

Since PERL_MAGIC_ext can be used by any extension, and since
sv_magicext can add more than one 'how' to an object, we should
protect our use of PERL_MAGIC_ext with 'signatures'.

• [PATCH] Safely store user locks in threads::shared by Jerry D. Hedden
• Re: [PATCH] Safely store user locks in threads::shared by Rafael Garcia-Suarez