Bump version to 5.1.19.
Bump version to 5.1.19.

luaposix/luaposix,ardje/luaposix,snegovick/luaposix,jimmyharris/luaposix,ardje/luaposix,rrthomas/luaposix,jimmyharris/luaposix,zevv/luaposix,snegovick/luaposix,rrthomas/luaposix,zevv/luaposix