Clarified windows guest machine support.
Clarified windows guest machine support.

Done at mitchellh's request.
kamigerami/vagrant,jfchevrette/vagrant,philoserf/vagrant,sax/vagrant,dharmab/vagrant,bheuvel/vagrant,zsjohny/vagrant,jhoblitt/vagrant,Sgoettschkes/vagrant,dustymabe/vagrant,zsjohny/vagrant,sni/vagrant,PatrickLang/vagrant,vamegh/vagrant,bdwyertech/vagrant,marxarelli/vagrant,mwarren/vagrant,dustymabe/vagrant,Endika/vagrant,mitchellh/vagrant,muhanadra/vagrant,ArloL/vagrant,gbarberi/vagrant,bshurts/vagrant,tomfanning/vagrant,gpkfr/vagrant,vamegh/vagrant,taliesins/vagrant,gitebra/vagrant,marxarelli/vagrant,gbarberi/vagrant,bryson/vagrant,tomfanning/vagrant,chrisroberts/vagrant,apertoso/vagrant,jean/vagrant,wangfakang/vagrant,loren-osborn/vagrant,teotihuacanada/vagrant,kamazee/vagrant,carlosefr/vagrant,lonniev/vagrant,ianmiell/vagrant,kalabiyau/vagrant,kamigerami/vagrant,pwnall/vagrant,mkuzmin/vagrant,gpkfr/vagrant,aaam/vagrant,chrisroberts/vagrant,krig/vagrant,Avira/vagrant,jmanero/vagrant,darkn3rd/vagrant,jberends/vagrant,aaam/vagrant,blueyed/vagrant,modulexcite/vagrant,ianmiell/vagrant,Chhunlong/vagrant,pwnall/vagrant,justincampbell/vagrant,wangfakang/vagrant,invernizzi-at-google/vagrant,marxarelli/vagrant,bshurts/vagrant,mitchellh/vagrant,jean/vagrant,tomfanning/vagrant,carlosefr/vagrant,philoserf/vagrant,krig/vagrant,PatrickLang/vagrant,sni/vagrant,krig/vagrant,myrjola/vagrant,petems/vagrant,senglin/vagrant,mwrock/vagrant,muhanadra/vagrant,bheuvel/vagrant,tjanez/vagrant,jfchevrette/vagrant,myrjola/vagrant,tbarrongh/vagrant,tbarrongh/vagrant,gpkfr/vagrant,janek-warchol/vagrant,petems/vagrant,tomfanning/vagrant,taliesins/vagrant,chrisvire/vagrant,muhanadra/vagrant,senglin/vagrant,mwarren/vagrant,jfchevrette/vagrant,bryson/vagrant,patrys/vagrant,tbriggs-curse/vagrant,doy/vagrant,doy/vagrant,jean/vagrant,apertoso/vagrant,jhoblitt/vagrant,jtopper/vagrant,taliesins/vagrant,dustymabe/vagrant,aneeshusa/vagrant,cgvarela/vagrant,johntron/vagrant,gitebra/vagrant,jmanero/vagrant,carlosefr/vagrant,tbarrongh/vagrant,chrisvire/vagrant,lukebakken/vagrant,janek-warchol/vagrant,Endika/vagrant,sni/vagrant,modulexcite/vagrant,gbarberi/vagrant,doy/vagrant,bdwyertech/vagrant,johntron/vagrant,dhoer/vagrant,cgvarela/vagrant,johntron/vagrant,fnewberg/vagrant,benizi/vagrant,tjanez/vagrant,kalabiyau/vagrant,dharmab/vagrant,chrisvire/vagrant,zsjohny/vagrant,Avira/vagrant,wangfakang/vagrant,sax/vagrant,bshurts/vagrant,h4ck3rm1k3/vagrant,jean/vagrant,nickryand/vagrant,modulexcite/vagrant,patrys/vagrant,modulexcite/vagrant,carlosefr/vagrant,Chhunlong/vagrant,invernizzi-at-google/vagrant,mwrock/vagrant,Chhed13/vagrant,cgvarela/vagrant,benh57/vagrant,ianmiell/vagrant,TheBigBear/vagrant,myrjola/vagrant,bshurts/vagrant,aneeshusa/vagrant,lonniev/vagrant,doy/vagrant,signed8bit/vagrant,mkuzmin/vagrant,bryson/vagrant,fnewberg/vagrant,crashlytics/vagrant,lonniev/vagrant,taliesins/vagrant,gbarberi/vagrant,stephancom/vagrant,h4ck3rm1k3/vagrant,nickryand/vagrant,patrys/vagrant,dharmab/vagrant,dhoer/vagrant,benizi/vagrant,Avira/vagrant,chrisvire/vagrant,Avira/vagrant,aneeshusa/vagrant,genome21/vagrant,kamazee/vagrant,benh57/vagrant,dharmab/vagrant,jhoblitt/vagrant,benh57/vagrant,PatOShea/vagrant,PatOShea/vagrant,loren-osborn/vagrant,mkuzmin/vagrant,tschortsch/vagrant,patrys/vagrant,kamigerami/vagrant,blueyed/vagrant,Chhed13/vagrant,mwrock/vagrant,chrisroberts/vagrant,darkn3rd/vagrant,genome21/vagrant,Sgoettschkes/vagrant,h4ck3rm1k3/vagrant,jmanero/vagrant,myrjola/vagrant,tbriggs-curse/vagrant,apertoso/vagrant,invernizzi-at-google/vagrant,sni/vagrant,jtopper/vagrant,stephancom/vagrant,genome21/vagrant,mkuzmin/vagrant,genome21/vagrant,bdwyertech/vagrant,janek-warchol/vagrant,lukebakken/vagrant,jfchevrette/vagrant,crashlytics/vagrant,ArloL/vagrant,teotihuacanada/vagrant,benizi/vagrant,kalabiyau/vagrant,wangfakang/vagrant,senglin/vagrant,marxarelli/vagrant,pwnall/vagrant,nickryand/vagrant,jberends/vagrant,fnewberg/vagrant,fnewberg/vagrant,PatOShea/vagrant,tjanez/vagrant,TheBigBear/vagrant,blueyed/vagrant,lonniev/vagrant,philoserf/vagrant,PatrickLang/vagrant,PatOShea/vagrant,loren-osborn/vagrant,zsjohny/vagrant,jberends/vagrant,jtopper/vagrant,stephancom/vagrant,muhanadra/vagrant,darkn3rd/vagrant,justincampbell/vagrant,Chhunlong/vagrant,kamazee/vagrant,tjanez/vagrant,jtopper/vagrant,apertoso/vagrant,justincampbell/vagrant,tschortsch/vagrant,kalabiyau/vagrant,philoserf/vagrant,chrisroberts/vagrant,signed8bit/vagrant,invernizzi-at-google/vagrant,mitchellh/vagrant,dhoer/vagrant,tbriggs-curse/vagrant,benizi/vagrant,stephancom/vagrant,petems/vagrant,bheuvel/vagrant,vamegh/vagrant,teotihuacanada/vagrant,jmanero/vagrant,justincampbell/vagrant,petems/vagrant,senglin/vagrant,bryson/vagrant,dhoer/vagrant,Chhunlong/vagrant,ArloL/vagrant,Endika/vagrant,johntron/vagrant,kamigerami/vagrant,gpkfr/vagrant,lukebakken/vagrant,cgvarela/vagrant,darkn3rd/vagrant,teotihuacanada/vagrant,PatrickLang/vagrant,Chhed13/vagrant,mwarren/vagrant,TheBigBear/vagrant,kamazee/vagrant,janek-warchol/vagrant,krig/vagrant,jberends/vagrant,nickryand/vagrant,tschortsch/vagrant,jhoblitt/vagrant,crashlytics/vagrant,ArloL/vagrant,h4ck3rm1k3/vagrant,TheBigBear/vagrant,sax/vagrant,Chhed13/vagrant,crashlytics/vagrant,Sgoettschkes/vagrant,Endika/vagrant,mitchellh/vagrant,signed8bit/vagrant,Sgoettschkes/vagrant,loren-osborn/vagrant,bheuvel/vagrant,aaam/vagrant,blueyed/vagrant,tbarrongh/vagrant,mwrock/vagrant,sax/vagrant,tbriggs-curse/vagrant,mwarren/vagrant,aaam/vagrant,ianmiell/vagrant,aneeshusa/vagrant,signed8bit/vagrant,gitebra/vagrant,tschortsch/vagrant,benh57/vagrant,gitebra/vagrant,bdwyertech/vagrant,vamegh/vagrant,lukebakken/vagrant,pwnall/vagrant,dustymabe/vagrant