Increace error detection in build script

Add 'verifysource' command to build to test if file in config.ini exist
in dir
Improve path handling

Expand ~ in paths to full absolute path in fields with multiple
paths and clean up paths with os.path.normpath()

Note: One issue, if the path is meant for a non-local filesystem, it
will still be expanded using the local user home dir if it uses the
tilde character, so to work around that, use a full path for a remote
filesystem.