ncurses 6.0 - patch 20170701

ncurses 6.0 - patch 20170701

+ modify update_getenv() in db_iterator.c to ensure that environment
  variables which are not initially set will be checked later if an
  application happens to set them (patch by Guillaume Maudoux).
+ remove initialization-check for calling napms() in the term-driver
  configuration; none is needed.
+ add help-screen to test/test_getstr.c and test/test_get_wstr.c
+ improve compatibility between different configurations of new_prescr,
  fixing a case with threaded code and term-driver where c++/demo did
  not work (cf: 20160213).
+ the fixes for Redhat #1464685 obscured a problem subsequently
  reported in Redhat #1464687; the given test-case was no longer
  reproducible.  Testing without the fixes for the earlier reports
  showed a problem with buffer overflow in dump_entry.c, which is
  addressed by reducing the use of a fixed-size buffer.
+ add/improve checks in tic's parser to address invalid input
  (Redhat #1464684, #1464685, #1464686, #1464691).
  + alloc_entry.c, add a check for a null-pointer.
  + parse_entry.c, add several checks for valid pointers as well as
    one check to ensure that a single character on a line is not
    treated as the 2-character termcap short-name.
+ fix a memory leak in delscreen() (report by Bai Junq).
+ improve tracemunch, showing thread identifiers as names.
+ fix a use-after-free in NCursesMenu::~NCursesMenu()
+ further amend incorrect calls for memory-leaks from 20170617 changes
  (report by Allen Hewes).