./configure not checking ruby

[Nakrez]

I tried to build slash on my laptop which did not have ruby.

The configure did not warn me about it, and make obviously thrown an error when executing gen scripts.

I think it may be good to check ruby on configure to warn the user.

[haileys]

I'm not sure about checking for Ruby in the configure script. When I release tarballs, they'll have generated source files (like src/lex.c, src/gen/*, etc.) pregenerated. So these are strictly development dependencies.

With that in mind, I should probably remove the check for flex from the configure script. Thoughts?

[Nakrez]

I think it would be better to check ruby, perl as well as flex, since they are used in developpement git tree, even if they are not used in release tarball.

This is my opinion, but the choice is yours.