Don't output "exec() finished with..." error message

It's useless because the result of the compiler is always evident (it outputs
either diagnostics or an exception stack trace)
Drop '-src' command line compiler option

Source file/directory paths should be specified separated by whitespaces in
between other command line arguments, as is everywhere in the world
Fix kotlinc command line usage information

Fix spelling, case, minor grammar
Minor, don't fire up Swing thread in CLI tests
Don't output full compiler FQ name on -printArgs
Use hand-written usage information printer

Copy-pasted from com.sampullara.cli.Args
Beautify kotlinc -help output
Output to the current directory by default ("-output .")