trac 15265: Additional functionality for Farey symbols.

Converted patch to git branch, expcept for two things:
- Tab whitespace in sl2z.hpp was not converted.
- Latex functionality for farey_symbols was not converted (because of
  conflicts with trac 14971 and Volker's suggestion on trac 15265).
trac 15265: Merge Hartmut's and David's solution for latex output of Farey symbols.
trac 15265: Revert capitalization for letters denoting groups.
trac 15265: correct mistakes done while converting to git branch.
trac 15265: Add some further examples and one test to _acton_ of elements of arithmetic groups.
trac 15265: Minor changes to farey.cpp and farey.hpp.
trac 15265: Minor changes to sl2z.cpp and sl2z.hpp.
trac 15265: Minor changes to farey_symbol.pyx
trac 15265: Additional change to farey.cpp.
trac 15265: various changes, finishing review.
Trac #14971: Better latex for Farey symbols

This patch adds a LaTeX rendering for Farey symbols (using the notation
from Kurth and Long's paper, http://arxiv.org/abs/0710.1835).

URL: http://trac.sagemath.org/14971
Reported by: davidloeffler
Ticket author(s): David Loeffler
Reviewer(s): Martin Raum
Trac #15265: Additional functionality for Farey symbols

The additional functionality included in this patch are:

- various possibilities for the tessellation of the fundamental domain
(Dedekind, coset, none)
- membership test via the Lang, Lim, Tan algorithm
- improved LaTeX output (via xymatrix)
- reduction to cusp
- identify cusp class

Added tests for LLT algorithm and reduction to cusp.

URL: http://trac.sagemath.org/15265
Reported by: hmonien
Ticket author(s): Hartmut Monien
Reviewer(s): David Loeffler, Martin Raum
Trac #14824: Frobenius endomorphism over p-adics

This patch provides a method {{{frobenius_endomorphism}}} which returns
the Frobenius endomorphism of a p-adic field.

Here is a small demo:

{{{
sage: K.<a> = Qq(5^3)
sage: Frob = K.frobenius_endomorphism()

sage: Frob
Frobenius endomorphism on Unramified Extension of 5-adic ... lifting a
|--> a^5 on the residue field
sage: Frob^12
Identity endomorphism of Unramified Extension of 5-adic Field ...

sage: Frob(a) = a.frobenius()
True
}}}

URL: http://trac.sagemath.org/14824
Reported by: caruso
Ticket author(s): Xavier Caruso
Reviewer(s): Kiran Kedlaya