octave: Enable opt-out of Java dependency

Mac OS X 10.10.1 Yosemite does not come with a Java Runtime Environment
bundled. Instead it has a sentinel program which alerts the user through
a message box that the runtime must be downloaded and installed.

The Autotools scripts detect this wrapper and allow to build the program
as if Java support was available. However, the programs are unusable
until a proper JRE is installed. This is particularily a problem when
installing other packages with Octave plugins, as the mkoctfile command
will now trip up a batch build.

This patch adds a --without-java option which is forwarded to the
configure script, as Octave is still usable without the Java support.
Thus, Octave can be installed on Yosemite without a JRE installed.
Thanks this is great. Would you mind adding the new dependency
````
depends_on :java if build.with? "java"
````
to the list of dependencies? The build will then abort if the JRE isn't installed.