lposix.c: improve documentation of posix.read
lposix.c: improve documentation of posix.read

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