Unimplemented features moved to their own exception (#1361)

Unimplemented features moved to their own exception

InternalCompilerError is an exception that really should be reserved for
actual internal errors of the compiler.  Unimplemented features can now
use either solUnimplemented( ) or, if it should be conditional, then
solUnimplementedAssert( ).

* Revert some unimplemented exceptions, add handlers

The jsonCompiler and CommandLineInterface needed handlers for the
new UnimplementedFeatureException, and some cases I had moved on to
the new exception were better treated as real internal compiler
errors.

* Standardize on "Unimplemented feature" message

solc/jsonCompiler.cpp

@@ -189,6 +189,10 @@ string compile(StringMap const& _sources, bool _optimize, CStyleReadFileCallback
 	{
 		errors.append(formatError(exception, "Internal compiler error", scannerFromSourceName));
 	}
+	catch (UnimplementedFeatureError const& exception)
+	{
+		errors.append(formatError(exception, "Unimplemented feature", scannerFromSourceName));
+	}
 	catch (Exception const& exception)
 	{
 		errors.append("Exception during compilation: " + boost::diagnostic_information(exception));