Update libsvm to 3.19, add --with-tools option

There are two commits. The first just updates the package to the newest version, the other add a `--with-tools`-option. The new options adds the tools that are included in the libsvm package if the flag is set.
The reason I used with tools is that not all of the tools require gnuplot and I thought it was more conservative to add the tools as an option than to force it on all new installs.