Fixed betterInstanceOf for Gecko
Fixed betterInstanceOf for Gecko

Some tests fail with SlimerJS...

Closes #732

sircelsiussexy/casperjs,jjyycchh/casperjs,vietch2612/casperjs,HienLeThi/Casperjs_Demo,soundyogi/casperjs,muntasir2000/casperjs,hlr1983/casperjs,jamesanthonyferguson/casperjs,cryptoquick/casperjs,hlr1983/casperjs,RobertoMalatesta/casperjs,RobertoMalatesta/casperjs,sircelsiussexy/casperjs,jjyycchh/casperjs,mcwonka/casperjs,cryptoquick/casperjs,mcwonka/casperjs,linkedin/casperjs,jamesanthonyferguson/casperjs,muntasir2000/casperjs,davidwhthomas/casperjs,singhdev/casperjs,vietch2612/casperjs,HienLeThi/Casperjs_Demo,hudl/casperjs,cryptoquick/casperjs,Andrey-Pavlov/casperjs,vietch2612/casperjs,n1k0/casperjs,mickaelandrieu/casperjs,mcwonka/casperjs,PeterWangPo/casperjs,PeterWangPo/casperjs,HienLeThi/Casperjs_Demo,cryptoquick/casperjs,sircelsiussexy/casperjs,casperjs/casperjs,HienLeThi/Casperjs_Demo,linkedin/casperjs,hexid/casperjs,pbrazdil/casperjs,singhdev/casperjs,mcwonka/casperjs,kyroskoh/casperjs,dj31416/casperjs,artillery/casperjs,muntasir2000/casperjs,istr/casperjs,JZL/casperjs,hudl/casperjs,singhdev/casperjs,muntasir2000/casperjs,pbrazdil/casperjs,davidwhthomas/casperjs,mickaelandrieu/casperjs,hudl/casperjs,joshuafcole/casperjs,istr/casperjs,hexid/casperjs,Andrey-Pavlov/casperjs,davidwhthomas/casperjs,casperjs/casperjs,Andrey-Pavlov/casperjs,artillery/casperjs,ravindrasingh22/casperjs,joshuafcole/casperjs,jefleponot/casperjs,artillery/casperjs,JZL/casperjs,joshuafcole/casperjs,flyHe/casperjs,kyroskoh/casperjs,jamesanthonyferguson/casperjs,alexbiehl/casperjs,casperjs/casperjs,ravindrasingh22/casperjs,artillery/casperjs,vietch2612/casperjs,jjyycchh/casperjs,dj31416/casperjs,JZL/casperjs,Andrey-Pavlov/casperjs,artillery/casperjs,alexbiehl/casperjs,alexbiehl/casperjs,mickaelandrieu/casperjs,hexid/casperjs,soundyogi/casperjs,jefleponot/casperjs,vietch2612/casperjs,jefleponot/casperjs,jamesanthonyferguson/casperjs,n1k0/casperjs,flyHe/casperjs,davidwhthomas/casperjs,casperjs/casperjs,jefleponot/casperjs,jefleponot/casperjs,hlr1983/casperjs,hudl/casperjs,HienLeThi/Casperjs_Demo,hexid/casperjs,RobertoMalatesta/casperjs,muntasir2000/casperjs,soundyogi/casperjs,soundyogi/casperjs,jjyycchh/casperjs,dj31416/casperjs,dj31416/casperjs,pbrazdil/casperjs,istr/casperjs,joshuafcole/casperjs,n1k0/casperjs,istr/casperjs,artillery/casperjs,sircelsiussexy/casperjs,RobertoMalatesta/casperjs,ravindrasingh22/casperjs,jamesanthonyferguson/casperjs,pbrazdil/casperjs,muntasir2000/casperjs,n1k0/casperjs,pbrazdil/casperjs,singhdev/casperjs,jjyycchh/casperjs,ravindrasingh22/casperjs,cryptoquick/casperjs,hlr1983/casperjs,singhdev/casperjs,jefleponot/casperjs,dj31416/casperjs,kyroskoh/casperjs,hlr1983/casperjs,PeterWangPo/casperjs,flyHe/casperjs,cryptoquick/casperjs,JZL/casperjs,linkedin/casperjs,PeterWangPo/casperjs,dj31416/casperjs,kyroskoh/casperjs,hexid/casperjs,joshuafcole/casperjs,n1k0/casperjs,hlr1983/casperjs,vietch2612/casperjs,ravindrasingh22/casperjs,mickaelandrieu/casperjs,mickaelandrieu/casperjs,pbrazdil/casperjs,alexbiehl/casperjs,kyroskoh/casperjs,linkedin/casperjs,davidwhthomas/casperjs,n1k0/casperjs,soundyogi/casperjs,sircelsiussexy/casperjs,Andrey-Pavlov/casperjs,linkedin/casperjs,mcwonka/casperjs,hexid/casperjs,PeterWangPo/casperjs,jjyycchh/casperjs,sircelsiussexy/casperjs,hudl/casperjs,davidwhthomas/casperjs,istr/casperjs,JZL/casperjs,alexbiehl/casperjs,mickaelandrieu/casperjs,RobertoMalatesta/casperjs,casperjs/casperjs,casperjs/casperjs,joshuafcole/casperjs,RobertoMalatesta/casperjs,soundyogi/casperjs,alexbiehl/casperjs,jamesanthonyferguson/casperjs,mcwonka/casperjs,ravindrasingh22/casperjs,Andrey-Pavlov/casperjs,PeterWangPo/casperjs,flyHe/casperjs,HienLeThi/Casperjs_Demo,JZL/casperjs,kyroskoh/casperjs,flyHe/casperjs,linkedin/casperjs,istr/casperjs,flyHe/casperjs