rsolve: simplify substitution of initial values
rsolve_hyper: fix issue 3745 [1/2]

    Return the correct number of arbitrary constants
    and refactor 'symbols' option handling.
rsolve_hyper: fix issue 3745 [2/2]

    Handle the case when the root of the denominator of
    the ratio y(n+1)/y(n) is symbolic: use direct comparison
    instead of max().  See also commit 39dc464 and issue 2408.

    Add test for issue 3745.
Merge pull request #2311 from skirpichev/3745-rsolve_hyper-fix

Fix issue 3745