Add updated bridges and spanning_trees to graph.py
Trac 11215: precision and other improvements
Minor docstring updates
Improved caching in monsky_washnitzer.py
Implemented k-closures for matroids.
More changes and fixes.
Merge branch 'master' into t/6637

* master: (557 commits)
  Updated Sage version to 6.2
  sage-cleaner: fix rm_rf on OS X
  Updated Sage version to 6.2.rc2
  fix grep
  skip checks if we do not use the system pkg-config
  fix indentation
  avoid potential race when creating pkg-config
  fix search path, add tests
  export variables
  fix permisions, reviewer patches
  fallback to system pkg-config if necessary
  Update top-level README.txt and installation guide to describe the new directory structure.
  reviewer changes
  updated readme
  #16196: rebased to #16232
  Updated Sage version to 6.2.rc1
  adding a doctest to make sure 13624 is fixed
  Trac #16210: Bug in is_hamiltonian: wrong exceptions are caught
  dev.abandon takes a mandatory argument
  remove tabs
  ...
Trac 11215: raise ValueError if the weight is not 2, don't warn about
precision for newforms attached to elliptic curves
Trac 11215: add doctests to test input checking
Trac 11215: documentation and examples to explain the relation to
modular symbols of elliptic curves
Fixed doctest.
Fixed type BC positive roots.
Merge branch 'public/ticket/15018' of trac.sagemath.org:sage into public/ticket/15018

Conflicts:
	src/sage/logic/logicparser.py
Merge branch 'public/ticket/15040' of trac.sagemath.org:sage into public/ticket/15040
Merge branch 'public/documentation/logic-15768' of trac.sagemath.org:sage into public/documentation/logic-15768

Conflicts:
	src/sage/logic/logic.py
Trac 11215: small improvements related to numterms
Merge remote-tracking branch 'trac/u/tmonteil/equality_vs_hash_for_braid_groups' into develop.6.2
Updated Sage version to 6.3.beta0
Merge branch 'public/ticket/10963-doc-distributive' of git://trac.sagemath.org/sage into 10963new

Conflicts:
	src/sage/schemes/elliptic_curves/ell_curve_isogeny.py
corrected conflict resolution