new backend executable names in 5.18

[Adrian Thurston]

Hi,

In version 5.18 the backend program has been split into several 
executables grouped by similarity of the output language.

rlgen-cd       C and D code
rlgen-dot      Graphviz
rlgen-java     Java (experimental)
rlgen-ruby     Ruby (new, experimental)

Also remember that when generating code the correct frontend language 
option must be given. The dot file generator does not care what language 
you are using.

The release is out, enjoy!

-Adrian