make_sandbox_from_installed: symbolic links creation errors

[Kenny Gryp]

(On ubuntu)

* When having mysql-mmm installed, the creation of the symbolic links fail because there are 2 matches of /usr/lib//mysql*:
/usr/lib/mysql
/usr/lib/mysql-mmm

gryp@lesktop:~/tmp$ make_sandbox_from_installed 5.1.54
ln: creating symbolic link `/home/gryp/tmp/5.1.54/lib/mysql': File exists
ln: creating symbolic link `/home/gryp/tmp/5.1.54/lib/mysql-mmm': File exists
error creating symbolic link (ln -s /usr/lib//mysql* /home/gryp/tmp/5.1.54/lib)

* /usr/lib64 is a symbolic link of /usr/lib causes errors too.

I have included a very basic patch that adds -f to 'ln', which solved at least my issues.