Handling file upload.
Handling file upload.

This is the result of the discovery work done by
@jimevans. I have:
- updated PhantomJS to provide a callback "onFilePicker"
- reworked his hack

Closes Issue #89.
yuanzhen/ghostdriver,acarpe/ghostdriver,detro/ghostdriver,amikey/ghostdriver,HelioGuilherme66/ghostdriver,testingbot/ghostdriver,HelioGuilherme66/ghostdriver,stevenliuit/ghostdriver,yuanzhen/ghostdriver,testingbot/ghostdriver,kuahyeow/ghostdriver,treejames/ghostdriver,jesg/ghostdriver,51ttw/ghostdriver,asolntsev/ghostdriver,amikey/ghostdriver,xsyntrex/ghostdriver,testingbot/ghostdriver,antoinereyt/ghostdriver,stevenliuit/ghostdriver,acarpe/ghostdriver,HelioGuilherme66/ghostdriver,jesg/ghostdriver,Vitallium/ghostdriver,antoinereyt/ghostdriver,kuahyeow/ghostdriver,treejames/ghostdriver,Lochlan/ghostdriver,detro/ghostdriver,xsyntrex/ghostdriver,asolntsev/ghostdriver,jesg/ghostdriver,jesg/ghostdriver,Lochlan/ghostdriver,testingbot/ghostdriver,detro/ghostdriver,51ttw/ghostdriver,Vitallium/ghostdriver