Support for debug builds (concatenation only)

Whitespace builds are still painful to debug.  Skipping the compiler altogether and simply concatenating sources is a better option for development and debugging.  By ommitting the `compile` option in a build config, the output is "uncompiled" - a straight concatenation of all sources in dependency order.
Merge pull request #2070 from tschaub/concatenate

Support for debug builds (concatenation only).