Add explicit cast with template parameters for GPMSA.
Add explicit cast with template parameters for GPMSA.

This resolves ambiguity that gave gcc-4.3.2 trouble.

briadam/queso,briadam/queso,roystgnr/queso,roystgnr/queso,briadam/queso,roystgnr/queso,briadam/queso,roystgnr/queso,roystgnr/queso,briadam/queso,roystgnr/queso