hgview #7316 add a --version command line option [validation pending]

hgview --version : displays the version of hgview and exit.

prioritynormal
typeenhancement
done in0.10.2
load0.500
load left0.000
closed by#f1ef01d91b39 [option] add a version option (closes #259595, #259572, #105330, #7316)