GetNewUnit: increase allowed number of open files to 16384 (#1392)

As of GCC 4.5 and Ifort ~10, the maximum allowed unit number is 2**31-1.
We are setting this to 16384, which is the limit on Eagle.

However, the OS may impose a limit:
- macos -- 256 (change with ulimit -n)
- linux -- 1024 typically (change with ulimit -n -- may require elevated permissions on clusters)
- windows -- probably 255 (`_setmaxstdio` to change)

modules/nwtc-library/src/NWTC_IO.f90

@@ -2207,7 +2207,11 @@ SUBROUTINE GetNewUnit ( UnIn, ErrStat, ErrMsg )
    INTEGER                                :: Un                                           ! Unit number
    LOGICAL                                :: Opened                                       ! Flag indicating whether or not a file is opened.
    INTEGER(IntKi), PARAMETER              :: StartUnit = 10                               ! Starting unit number to check (numbers less than 10 reserved)
-   INTEGER(IntKi), PARAMETER              :: MaxUnit   = 99                               ! The maximum unit number available (or 10 less than the number of files you want to have open at a time)
+   ! NOTE: maximum unit numbers in fortran 90 and later is 2**31-1.  However, there are limits within the OS.
+   !     macos -- 256  (change with ulimit -n)
+   !     linux -- 1024 (change with ulimit -n)
+   !     windows -- 512 (not sure how to change -- ADP)
+   INTEGER(IntKi), PARAMETER              :: MaxUnit   = 1024                             ! The maximum unit number available (or 10 less than the number of files you want to have open at a time)
    CHARACTER(ErrMsgLen)                   :: Msg                                          ! Temporary error message