Retry file lock/read operations on EIO errors

As seen on MacOS, an SMB shared file can cause the Mac SMB client to report EIO
error on locked-file read or lock attempts. So retry.

src/xpdev/filewrap.h

@@ -145,7 +145,7 @@
 #define FCLOSE_OPEN_FILE(x)	do { if((x) != NULL) { fclose(x); (x) = NULL; } } while(0)
 
 // These errno values should trigger sopen() and lock() retries, within limits
-#define FILE_RETRY_ERRNO(x) ((x)==EACCES || (x)==EAGAIN || (x)==EDEADLOCK || (x)==EBUSY)
+#define FILE_RETRY_ERRNO(x) ((x)==EACCES || (x)==EAGAIN || (x)==EDEADLOCK || (x)==EBUSY || (x)==EIO)
 
 /**************/
 /* Prototypes */