[Dart] Sweeping Dart changes

[Brad King]

>   - Dart installation defaults are stored in
> DartRoot/Source/Client/DartDefaults.conf, as backup for non-specified
> Dart options
The new config format looks nice.  One thought that has crossed my mind is
this:

CMakeCommand:  at CMAKE_COMMAND at 
MakeCommand:  at MAKECOMMAND at  
CVSCommand:  at CVSCOMMAND at  
TclshCommand:  at TCL_TCLSH at  
JavaCommand:  at JAVACOMMAND at  
ScpCommand:  at SCPCOMMAND at  
GunzipCommand:  at GUNZIPCOMMAND at  
CompressionCommand:  at COMPRESSIONCOMMAND at  
CompressionType:  at COMPRESSIONCOMMAND at  

For non-CMake uses of Dart, these values are a pain to specify.  In the
past, I've included logic in the config file to find these values.  Now
that the config file isn't sourced, this won't work.  Almost all of the
time appropriate defaults can be found by inspecting the system path or
even by just invoking the programs without the full path.  Is this
available already, or can it be added?

-Brad