dpkg-gensymbols: be more explicit in warning about new/lost libraries

dpkg-gensymbols: be more explicit in warning about new/lost libraries

* scripts/Dpkg/Shlibs/SymbolFile.pm: Replace has_new_libs(),
has_lost_libs(), has_new_symbols() and has_lost_symbols() by
corresponding get_* functions.
* scripts/dpkg-gensymbsols.pl: Display list of new/lost libs. Also
display list of lost symbols when wildcards symbols have been
used.
* scripts/t/200_Dpkg_Shlibs.t: Adjust test suite to API change.