don't force Chrome Frame for all installations

    
There's already a plugin[1] which enables support for this, and it also
provides more configuration options. The user may not want to code the
'chrome=1' and thereby force CF for all installations. Also, the plugin
allows the install to send the CFInstall javascript launcher.
    
[1] https://wiki.jenkins-ci.org/display/JENKINS/Chrome+Frame+Plugin