Add real-conversion constructor.

Add constructors for default/value-initialization and conversion from a
real value.  Add corresponding test.  Remove calls to
value-initialization from previous tests.
Add component-list constructors and cross-philosophy conversions

- Change single-real constructor in "complex_it" to take a list of
components
instead.
- Add component-list constructor to "complex_rt" (recursive case).
- Add constructor and operator (both explicit) in "complex_rt" (both
cases) for
converting to or from "complex_it."  (The previous item needs these.)
- Remove some verbiage from the old constructors in "complex_rt"
(recursive
case).
- Correct some spelling errors.