trac #16373: OA(18,273), OA(12,474), OA(33,993)
allow some trigonometric functions to take complex as input

This fixes bugs in arctan, arcsec, arccsc, where complex numbers as input
would result in an AttributeError
add couple of doctests for complex input
Need to convert to complex only
fix unneeded line number in doctest
trac #16476: new (25,4,1) DF and clean bibd.py
trac #16476: Additional check
trac #16373: merge #16361

Conflicts:
	src/sage/combinat/designs/database.py
Use git's push url in the Developer's Guide
Trac #16482: Update developer manual for git's push-url feature

Related to [https://github.com/sagemath/git-trac-command/pull/7].

URL: http://trac.sagemath.org/16482
Reported by: emassop
Ticket author(s): Erik Massop
Reviewer(s): Volker Braun
Trac #16439: Allow inverse trig functions to all take complex input

Where by complex I mean `complex` Python type.
{{{
sage: arccos(1+2*i)
arccos(2*I + 1)
sage: arccos(CC(1,2))
1.14371774040242 - 1.52857091948100*I
sage: arccos(CDF(1,2))
1.1437177404 - 1.52857091948*I
sage: arccos(complex(1,2))
<snip>
TypeError: Unable to convert x (='(1+2j)') to real number.
}}}
Presumably there are others of this type.  Related:
{{{

sage: arcsec(-0.992725195401)
NaN
sage: arcsec(float(-0.992725195401))
<snip>
    732         if parent is float:
    733             return math.acos(1/x)
--> 734         return (1/x).arccos()
    735
    736     def _eval_numpy_(self, x):

AttributeError: 'complex' object has no attribute 'arccos'
}}}
but this may or may not be dealt with at #13246.

URL: http://trac.sagemath.org/16439
Reported by: kcrisman
Ticket author(s): Punarbasu Purkayastha
Reviewer(s): Karl-Dieter Crisman, Ralf Stephan
Trac #16373: OA(18,273), OA(12,474), OA(33,993)

Okayyyyyyyyyyyyyyy... I think this is the end of this long sequence of
constructions, now `:-P`

Nathann

URL: http://trac.sagemath.org/16373
Reported by: ncohen
Ticket author(s): Nathann Cohen
Reviewer(s): Vincent Delecroix
Trac #16476: New difference family (25,4,1) and cleanup in bibd.py

In the construction of Stinson book the `BIBD(25,4,1)` comes from a
difference family so we can just add it to the database. Moreover the
function `PBD_4_5_8_9_12` previously failed for `v=4,5,8,9,12` where the
trivial answer `[range(v)]` just fits.

URL: http://trac.sagemath.org/16476
Reported by: vdelecroix
Ticket author(s): Vincent Delecroix
Reviewer(s): Nathann Cohen