govc: fix build.sh git tag injection

Merge pull request vmware#2014 from dougm/docs

Update docs for 0.23 release

Merge pull request vmware#1997 from dougm/issue-1996

govc: support raw object references in import.ova NetworkMapping

Merge pull request vmware#1586 from dougm/rest-session

vapi: return info with current session query