filter: rv doesn't build with "withcv" tag

[Trek Hopton]

The build tags in filter/release.go need to be changed so that rv can be built with the tag withcv.

This is required for turbidity software.

This was obviously a mistake when the build tags were inverted from nocv to withcv.

[Trek Hopton]

Merged in withcv-fix (pull request #509)

filter: change build tags to allow build withcv

Resolves Issue #412

→ <<cset a978e27e4fab>>