Log message

Some more features related to powers and roots

* made mpc_pow_int fast and more accurate for a pure real or pure imaginary
argument
* implemented powm1() for accurate calculation of x^y - 1
* added docs and tests for expm1(), and fixing the wrong value of expm1(0) (!)
* made nthroot() optionally compute any of the nonprincipal roots
* renamed nthroot() -> root() for brevity, keeping nthroot() as an alias
* more elaborate docstring for root()
* implemented unitroots(), computing all roots of unity (optionally primitive
only)
* implemented cyclotomic(), evaluating cyclotomic polynomials

	Modify	/trunk/mpmath/__init__.py	diff
	Modify	/trunk/mpmath/function_docs.py	diff
	Modify	/trunk/mpmath/functions.py	diff
	Modify	/trunk/mpmath/libintmath.py	diff
	Modify	/trunk/mpmath/libmpc.py	diff
	Modify	/trunk/mpmath/tests/test_functions.py	diff