release: update to use git instead of svn:

release.sh:

• Bump the version number.
• Default VCSCMD to '/usr/local/bin/git clone'.
• Rename SVN* variables to GIT* equivalents.
• Remove dead code to inject a trailing '/' between two variables.
• Remove SRC_FORCE_CHECKOUT.
• Exit if the build host does not have devel/git installed.
• Install devel/git in the build chroot(8) for newvers.sh.

release.conf.sample:

• Update sample configuration variables to the git equivalent.

relnotes-search.sh:

• Remove script. It is specifically for use with svn.

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