Modified /ligo/cdscfg and /opt/cdscfg setup scripts to allow a user to use an alternate userapps checkout.

To use, check out a private copy of the userapps repository into your home directory and then:

source $HOME/userapps/etc/userapps-env.sh 

or set the PRIVATE_USERAPPS environment variable and source the top-level CDS configuration script:

export PRIVATE_USESRAPPS=$HOME/userapps
source /ligo/cdscfg/stdsetup.sh