git-cvsserver: clarify directory list

The documentation and error messages for git-cvsserver include some references to a "whitelist" that is not otherwise included in the documentation. When different parts of the documentation do not use common language, this can lead to confusion as to how things are meant to operate. Further, the word "whitelist" has cultural implications that make its use non-inclusive. Thankfully, we can remove it while increasing clarity. Update Documentation/git-cvsserver.txt in a similar way to the previous change to Documentation/git-daemon.txt. The optional '<directory>...' list can specify a list of allowed directories. We refer to that list directly inside of the documentation for the GIT_CVSSERVER_ROOT environment variable. While modifying this documentation, update the environment variables to use a list format. We use the modern way of tabbing the description of each variable in this section. We do _not_ update the description of '<directory>...' to use tabs this way since the rest of the items in the OPTIONS list do not use this modern formatting. A single error message in the actual git-cvsserver.perl code refers to the whitelist during argument parsing. Instead, refer to the directory list that has been clarified in the documentation. Signed-off-by: Derrick Stolee <derrickstolee@github.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>