add "git trac" to the developer manual
splitting the walkthrough in a local and a remote part
also mention the cheat sheet
add missing checkout command
Make PPL build with GCC 4.9 (C++ name lookup issue, s/ptrdiff_t/std::ptrdiff_t).
Make Lcalc (1.23) build with GCC 4.9 (move default parameter from definition to declaration).

This patch just fixes the single instance GCC 4.9 currently complains about.

Clang is more picky, and will need further fixes (including moving a few more
invalid default parameters in function *definitions* into *declarations*
instead); see:

  http://trac.sagemath.org/ticket/12437
reviewer suggestions
fix links
add section on how to rebuild sage
use git trac print instead of get
Significant reconfiguration and some rewrite of developer guide.

This is mainly to clarify the role of git-trac and the dev scripts,
but also includes some reorganization and introductory material.
Add info about sage -dev -h to the developer guide.
Fixed hyperlinks and added minor information about compiling Sage
be clear about what is recommended
Merge branch 'develop' into t/16208/ticket/16208
document patches
Trac #16208: Make Sage (6.1.1/6.2.beta*) build with GCC 4.9

[http://gcc.gnu.org/gcc-4.9/ GCC 4.9.0] has been released on April 22nd
2014.

Due to stricter conformance to the C++ standard, both the current stable
release of Sage, 6.1.1, and the current development release, 6.2.beta8,
won't build with GCC 4.9.

Luckily only two Sage packages, namely Lcalc (1.23) and PPL (1.1), are
affected, and small patches which don't change any functionality are
sufficient to let Sage build with the new GCC.  (The same patch(es)
apply to both Sage 6.1.1 and 6.2.beta8.)

URL: http://trac.sagemath.org/16208
Reported by: leif
Ticket author(s): Leif Leonhardy
Reviewer(s): Volker Braun
remove tabs
Trac #16030: Use "git trac" in the developer guide

URL: http://trac.sagemath.org/16030
Reported by: vbraun
Ticket author(s): Volker Braun, Karl-Dieter Crisman
Reviewer(s): Ralf Stephan, Volker Braun, Karl-Dieter Crisman