Fix legacy iterator and membertest pattern regressions.

* da/compiler/parser.py(Parser.generic_visit): mark as query.

* da/compiler/pygen.py:

  -(PythonGenerator.visit_DomainSpec): handle legacy stand-alone
   patterns.

  -(PythonGenerator.visit_ComprehensionExpr): don't replace the
   condition list on the last generator, extend it.
Allow setting compiler options in source file.

If the first non-empty line of the input source file is a string, parse
it as command line options. Actual command line options override
settings in the source file.

* da/compiler/dast.py(Program._compiler_options): new property, to store
  compiler options from the source file.

* da/compiler/incgen.py: normalize option names.

* da/compiler/parser.py:

  -(Parser.get_option): new method, returns the effective value for a
  given option.

  -(Parser.parse_module_header): new method.

* da/compiler/ui.py(main): normalize option names and default values.

* da/compiler/utils.py:

  -(Namespace): new class.

  -(OptionsManager): new class, wrapper around in-file options and
   command line options.