[with patch, positive review] Faster basis and discriminants of a Hecke algebra

[robertwb]

Followup to #6768, uses algorithm at ​http://wiki.sagemath.org/days17/projects/presagedays/discussion

[robertwb]

Also discriminants.

[was]

REFEREE REPORT:

1. Awesome trace of product trick!

2. I think the following range must start at 1 -- otherwise this is potentially (in theory) a major bug:

   span = [self.hecke_operator(n) for n in range(2, bound+1) if not self.is_anemic() or gcd(n, level) == 1] 
   

3. "eisenstein" should be capitalized below:

    	1182	        Returns whether self is cuspidal, i.e. has no eisenstein part.
   

4. The patch doesn't seem to apply cleanly to 4.1.2.alpha1:

   Hunk #4 FAILED at 214
   1 out of 6 hunks FAILED -- saving rejects to file sage/modular/hecke/algebra.py.rej
   abort: patch failed to apply
   

[was]

Apply these:

trac_6911-referee-replace_other_patch-apply_only_this.patch
trac_6911-referee_followup_that_fixes_some_bugs.patch 

[mvngu]

Merged patches in this order:

1. trac_6911-referee-replace_other_patch-apply_only_this.patch
2. trac_6911-referee_followup_that_fixes_some_bugs.patch