get-bytevector-all does not work on pipes about mosh-scheme HOT 4 OPEN

Please find attached a rough patch for this.
Possible issues with the patch are:
1.  Adds an extra fstat() syscall to every call to get-bytevector-all.
2.  No Windows support, only tested in Linux.
3.  isFIFO() doesn't handle errors, not sure how to go about this?
4.  Adds 2 private methods to FileBinaryInputPort

If you think this approach is OK I can write a test for it in tests/process.scm.

Cc me.

I feel we need additional return value on File::size() at OSCompat.cpp.

ie.) Currently, we have 2 condition for File::size() return value:

-1 = Invalid file descriptor
otherwise = File size

We need additional one;

-2 = Object has indefinite size (eg. pipes)

An updated patch is attached implementing this approach plus a test in 
tests/process.scm.

Thank you for your patch.
Will you define or enum the -2 value?