Add support of wildcard entries in symbols files

Add support of wildcard entries in symbols files

* scripts/Dpkg/Shlibs/SymbolFile.pm (load): Parse *@<version> symbols names as
wildcards and not as regular symbols.
* scripts/Dpkg/Shlibs/SymbolFile.pm (merge_symbols): Use information
provided by wildcards entries when new symbols are added.
* scripts/dpkg-gensymbols.pl: Disable some checks which can't be done when
symbols files have been generated with the help of wildcard entries.
* man/dpkg-gensymbols.1: Update the manual page to explain how to use
wildcard entries.