Remove parallel build Travis testing for Perl

Best not to use resources where not needed - non parallel builds for
Perl are similar in run timme to other languages.
Mark potential incompatibility in changes notes
Warning suppression in director_abuse testcase

Document small observation about director_abuse testcase too.
CurrentClass and ClassName refactor in Perl

Remove replication of CurrentClass in lang.cxx.
Also replace ClassName macro in perl module with real code.
Cosmetic code formatting
Cosmetic perl director code changes

To fit in with usual coding style for multiple lines of code generation.