Please describe the problem:
When adding a user with users-admin, files from /etc/skel (typically .bashrc and
.bash_profile) are copied to the specified home directory, overwriting those
files in the home directory without warning.   

Steps to reproduce:
1. Use users-admin to add a new user, specifying a home directory that already
exists.


Actual results:
If .bashrc and .bash_profile already exist in the specified home directory,they
are overwritten without warning. 

Expected results:
A warning dialog might be helpful. ("Pre-existing configuration files in
/home/foo will be overwritten. Continue?")

Does this happen every time?
Yes.

Other information:
When /home/foo already exists, one might reasonably expect users-admin to behave
like "useradd -d /home/foo foo", which does not overwrite /home/foo/.bashrc,
etc.   With useradd, an additional flag (-m) must be explicitly given in order
for /etc/skel files to be copied.