+ several fixes for gcc8 strict compiler warnings.
+ fix a typo in comments (Aaron Gyes).
+ add nsterm-build309 to replace nsterm-256color, assigning the latter
as an alias of nsterm, to make mouse work with nsterm-256color -TD
+ base gnome-256color entry on "gnome", not "vte", for consistency -TD
+ updates for configure macros from work on tin and xterm:
+ CF_GNU_SOURCE, allow for Cygwin's newlib when checking for the
_DEFAULT_SOURCE symbol.
+ CF_VA_COPY, add fallback check if neither va_copy/__va_copy is
supported, to try copying the pointers for va_list, or as an array.
Also add another fallback check, for __builtin_va_copy(), which
could be used with AIX xlc in c89 mode.
+ add configure check to distinguish clang from gcc to eliminate
warnings about unused command-line parameters when compiler warnings
are enabled.
+ improve behavior when updating terminfo entries which are hardlinked
by allowing for the possibility that an alias has been repurposed to
a new primary name.
+ fix some strict compiler warnings based on package scripts.
+ further fixes for configure check for working poll (Debian #676461).
+ for term-driver configuration, ensure that the driver pointer is
initialized in setupterm so that terminfo/termcap programs work.
+ amend fix for Debian #542031 to ensure that wattrset() returns only
OK or ERR, rather than the attribute value (report by Miroslav
Lichvar).
+ reorder WINDOWLIST to put WINDOW data after SCREEN pointer, making
_nc_screen_of() compatible between normal/wide libraries again (patch
by Miroslav Lichvar)
+ review/fix include-dependencies in modules files (report by Miroslav
Lichvar).
