Porting/Maintainers.pl - Move most of ext/ and lib/ into _PERLLIB

Most ext/ and lib/ entries in %Modules only list a single folder or a couple
of files sharing the same basename and specify no more information other
than UPSTREAM => 'blead'. This information can be more succinctly conveyed
by a line in _PERLLIB.

Only the following ext/ and lib/ entries in %Modules now remain:

B (has EXCLUDED files)
B::Concise (has a MAINTAINER)
VMS::DCLsym (has a MAINTAINER)
VMS::Stdio (has a MAINTAINER)
Win32CORE (has a MAINTAINER)
warnings (has a MAINTAINER and files from various places)

The middle four can probably move too if it is deemed that the MAINTAINER
information is not useful.