Fix the issue tigervnc-server and -viewer cannot be installed together
when DOCS=on because both ports install LICENSE_FILE into the same place.
Also, following changes are made.
- bump PORTREVISION due to plist & dependency change
- do not build tests, it introduces unnecessary dependencies on fltk
- add missing dependency on devel/m4
- remove unnecessary dependency on x11-toolkits/fltk
Approved by: portmgr (miwi)