Fortran, typeprint: Decrease level of details when printing elements of a structure.

According to the typeprint's description, the level of details is
decreased by one for the typeprint of elements of a structure.

Before:
(gdb) ptype t3v
type = Type t3
    integer(kind=4) :: t3_i
    Type t2
        integer(kind=4) :: t2_i
        Type t1
            integer(kind=4) :: t1_i
            real(kind=4) :: t1_r
        End Type t1 :: t1_n
    End Type t2 :: t2_n
End Type t3

After:
(gdb) ptype t3v
type = Type t3
    integer(kind=4) :: t3_i
    Type t2 :: t2_n
End Type t3

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

gdb/Changelog:
	* f-typeprint.c (f_type_print_base): Decrease show by one.

gdb/testsuite/Changelog:
	* gdb.fortran/type.f90: Add nested structures.
	* gdb.fortran/whatis-type.exp: Whatis/ptype nested structures.
	* gdb.fortran/derived-type.exp: Adapt expected output.
	* gdb.fortran/vla-type.exp: Adapt expected output.