This commit strengthens an assertion so that it makes sure that a pointer is not null.
Moreover, `isLocalVariable(variable)` is now positively asserted, following the error message.
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
This commit adds support for a standard do <statement> while <expr>;
form of statement. While loops were already being supported; supporting
a do/while loop mostly involves reusing code from while loops but putting
the conditional checking last.
