Make the File.open constructor use read-only mode (#2568)
Make the File.open constructor use read-only mode (#2568)

Use @ponyint_o_rdonly rather than _rdwr in the calls to @open and
@_open.
kulibali/ponyc,ponylang/ponyc,jemc/ponyc,Theodus/ponyc,sgebbie/ponyc,dipinhora/ponyc,sgebbie/ponyc,cquinn/ponyc,sgebbie/ponyc,kulibali/ponyc,sgebbie/ponyc,dipinhora/ponyc,Theodus/ponyc,jemc/ponyc,kulibali/ponyc,CausalityLtd/ponyc,CausalityLtd/ponyc,CausalityLtd/ponyc,Theodus/ponyc,Theodus/ponyc,cquinn/ponyc,ponylang/ponyc,cquinn/ponyc,Theodus/ponyc,jemc/ponyc,kulibali/ponyc,dipinhora/ponyc,cquinn/ponyc,sgebbie/ponyc,ponylang/ponyc