Log Message:
webkit-gtk: Avoid to depends on flex and minor cleanup

- The flex requirements can be just satisfied via USE_TOOLS (the
  version was from older webkit-gtk-s and it should be just a tool
  dependency).
- No need to specify `:build' in USE_TOOLS, it is already the default
- Update the comment regarding PYTHON_VERSIONS_INCOMPATIBLE definition

Bump PKGREVISION