Unable to save file in xspec v11

Glenn Morris reported that when xspec v11 is built using gcc4 then the save command will not allow an existing filename to be overwritten. This turned out to be because in this case the Fortran OPEN command returns an IOSTAT=1, not IOSTAT=128 as per gcc3. This breaks the code in OPENWR in sys.lnx and sys.darwin. Fixed in v11.3.2ah by using an INQUIRE in these two files to check for a pre-existing file.

Note that the sys.* options are labelled by operating system however all those running gcc should be the same (eg sys.lnx and sys.darwin).