[with patch, positive review] improved orthogonal functions

[fwclarke]

The defects in the code for the hermite function in sage/functions/orthogonal_polys.py which were noted and corrected in #2336 apply equally to the other functions in that file.

The attached patch applies the same fix that worked for hermite to the following functions:

chebyshev_T, chebyshev_U, gen_laguerre, gen_legendre_P, gen_legendre_Q, jacobi_P, laguerre, legendre_P, legendre_Q, ultraspherical

This allows these polynomials to take much more general arguments; see the examples given for legendre_P.

The functions:

gen_legendre_P, gen_legendre_Q, legendre_Q

no longer yield a string representing a Maxima expression when the argument is a variable.

For m > n the function gen_legendre_Q(n, m, x) has to be computed independently of Maxima. This part of the code may need improving.

The introductory documentation has not been changed.

[mhansen]

Looks good to me. All the tests pass, and the patch definitely simplifies the code.

[mabshoff]

Merged in Sage 3.0.2.rc0