Use discovered asciidoc/a2x to get the version.
Use discovered asciidoc/a2x to get the version.

Use the discovered asciidoc/a2x executables to get their respective version
instead of the hardcoded "asciidoc" and "a2x" names.  Catch an AttributeError in
case the discovered names are None.

marcecj/scons_asciidoc