(gud-menu-map): Add jdb support for "run".

(gud-menu-map): Add jdb support for "run".
(gud-jdb-find-source-using-classpath): Use 'identity.
(gud-jdb-marker-filter): Marker regexp and filename filtering change to
support a backwards-incompatible change in Sun's jdb line number display in
SDK versions 1.4.
(gud-format-command): gud-find-class now requires two parameters (file and
linenumber).
(gud-find-class): Bulk of the change related to using c-syntactic symbols
to locate nested class declarations in java sources visited by java-mode
(cc-mode).