Update build-client.xml

set git_branch to ENV.GIT_BRANCH and added ENV.GIT_COMMIT to the version.properties as git_commit
Access checks and DownloadCache directory fix
Merge branch 'master' of git@github.com:smbarbour/MCUpdater.git
Changed string comparison operators
Tray icon now restores MCU on double-click
Added "hard" update option
Default behavior changed to not delete instance contents.
WIP Instancing
Further work on instancing
New classes
Instancing ready for production.