Open web address page in a browser.
page should be the full path, such as "http://www.zimbu.org".
For ZWT you need to use something like "http://localhost:8884/".
Does not wait for the browser to finish, uses SYS.shellBackground().
Uses $BROWSER when it is set.
Otherwise, on Mac OS the "open URL" command is used.
On MS-Windows the default browser is used. On other systems
the following commands are tried: "google-chrome", "firefox", "safari",
"opera" and "ie". The first one that can be found in $PATH is used.
When none is found or execution fails then FAIL is returned.