- also drop various unused time options from src/OpenFOAM/include

Oriented somewhat on dictionary methods.

Return the argument string associated with the named option:
    Info<< "-foo: " << args.option("foo") << nl;

Return true if the named option is found
    if (args.optionFound("foo")) ...

Return an IStringStream to the named option
    old:      value = readScalar(IStringStream(args.options()["foo"])());
    newer:    value = readScalar(args.optionLookup("foo")());
    also:     List<scalar> lst(args.optionLookup("foo")());

Read a value from the named option
    newest:   value = args.optionRead<scalar>("foo");

Read a value from the named option if present.
    old:  if (args.options().found("foo"))
          {
              value = readScalar(IStringStream(args.options()["foo"])());
          }
    new:  args.optionReadIfPresent("foo", value);

Read a List of values from the named option
    patches = args.optionReadList<word>("patches");

Didn't bother adding optionReadListIfPresent<T>(const word&), since it
probably wouldn't be common anyhow.

- made const_iterator::operator* and const_iterator::operator() const only
- added const versions of iterator::operator* and iterator::operator()

comments

- Read a bracket-delimited list, or handle a single value as list of size 1.
  Mostly useful for handling command-line arguments.
  eg,
      if (args.options().found("patches"))
      {
          patches = readList<word>(IStringStream(args.options()["patches"])());
      }
  can handle both of these:
      -patches  patch0
      -patches \( patch1 patch2 patch3 \)

- use isFile() instead of exists() for file-checking

- change name of environment variable from $WM_OS -> $WM_OSTYPE
  as a better description