default values of maps must be copied
default values of maps must be copied

Otherwise the same underlying map is used and operations on option.value
also change option.defaultValue. Therefore a valid comparison of .value
and .defaultValue is impossible.

conseweb/go-flags,fuchsia-mirror/third_party-github.com-jessevdk-go-flags,cmars/tools,jessevdk/go-flags,cmars/tools,fuchsia-mirror/third_party-github.com-jessevdk-go-flags,svent/go-flags,cmars/tools,abates/go-flags,sysbot/go-flags,sourcegraph/go-flags,conseweb/go-flags,FactomProject/go-flags,abates/go-flags,jessevdk/go-flags,FactomProject/go-flags,svent/go-flags,cmars/tools,sourcegraph/go-flags,sysbot/go-flags