Add support for jdb (Java debugger).

Add support for jdb (Java debugger).
(jdb): New function.
(gud-jdb-history): New variable.
(gud-jdb-directories): New variable.
(gud-jdb-source-files): New variable.
(gud-jdb-build-source-files-list): New function.
(gud-jdb-package-of-file): New function.
(gud-jdb-class-source-alist): New variable.
(gud-jdb-build-class-source-alist): New function.
(gud-jdb-massage-args): New function.
(gud-jdb-find-source-file): New function.
(gud-jdb-marker-filter): New function.
(gud-jdb-find-file): New function.
(gud-jdb-command-name): New variable.
(gud-perldb-command-name): Variable renamed from perldb-command-name.