refactor CGITempFile::find_tempdir to use File::Spec

File::Spec has a tmpdir function that is platform independent so we
can replace the pre-re-invented wheel here with another solution.
File::Spec is core and is already required in the Makefile.PL so
there is no change there

related: #91 [rt.cpan.org #71799] - really you should care about
the internals of where temp files are stored, so i'm taking the
decision to abstract this away to something cleaner
resolve #109 [rt.cpan.org #81935] - change distname

from CGI.pm to CGI - this will allow various CPAN tools to query
the dist without having exceptions for CGI.
bump version to 4.03_03 and make consistent

CGI::Cookie had it's own version for some reason, make it the same
as the rest of the dist