ncurses 5.6 - patch 20080816

ncurses 5.6 - patch 20080816

+ add configure option --enable-weak-symbols to turn on new feature.
+ add configure-check for availability of weak symbols.
+ modify linkage with pthread library to use weak symbols so that
  applications not linked to that library will not use the mutexes,
  etc.  This relies on gcc, and may be platform-specific (patch by Dr
  Werner Fink).
+ add note to INSTALL to document limitation of renaming of tic library
  using the --with-ticlib configure option (report by Dr Werner Fink).
+ document (in manpage) why tputs does not detect I/O errors (prompted
  by comments by Samuel Thibault).
+ fix remaining warnings from Klocwork report.