fixContext: remove non-existant global '$page'
port type could be changed even if port is linked

renderPortsForObject: render form controls even if port is linked
getExistingPortTypeOptions: check if port is linked and select only compatible types
handlePopupPortLink: fix broken link in succss msg
dont return showError* result from ophandlers

this technique saved one line of code, but obscured the prototype of
ophandlers and showError* functions.

Changed all occurrences of 'return show*' to 'show*; return;' pairs
0.20.6: cut the release