Fortran, typeprint: Take level of details into account when printing elements of a structure.

According to the typeprint's description, elements of a structure
should not be printed when show is < 1.
This variable is also used to distinguish the level of details
between "ptype" and "whatis" expressions.

Before:
(gdb) whatis t1v
type = Type t1
    integer(kind=4) :: t1_i
    real(kind=4) :: t1_r
End Type t1

After:
(gdb) whatis t1v
type = Type t1

2016-05-25  Bernhard Heckel  <bernhard.heckel@intel.com>

gdb/Changelog:
	* f-typeprint.c (f_type_print_base): Don't print fields when show < 0.

gdb/testsuite/Changelog:
	* gdb.fortran/whatis_type.exp: Adapt expected output.