trac #16868: A real difference matrix has k columns
trac #16870: Use float("inf") instead of Infinity
trac #16870: remove an import
trac #16868: Mb was initialized twice
Fix incorrect help for reinstalling a package
trac #16875: move imports
trac #16875: set the cache when we call difference_matrix
Trac #16868: A real difference matrix has k columns

Change Sage's standard to be coherent with OA which have k columns. This
is much easier to work with on a computer, for it is much easier to add
a row to a matrix than to add a column. And this is what we have to do
most of the time.

Nathann

URL: http://trac.sagemath.org/16868
Reported by: ncohen
Ticket author(s): Nathann Cohen
Reviewer(s): Vincent Delecroix
Trac #16870: Use float("inf") instead of Infinity

Yes, it makes a difference in speed `T_T`

Nathann

URL: http://trac.sagemath.org/16870
Reported by: ncohen
Ticket author(s): Nathann Cohen
Reviewer(s): Vincent Delecroix
Trac #16875: Move 'import' in orthogonal_array()

Win some perf with a couple of improvements. Nothing fantastic, but
still worth taking.

Nathann

Before
{{{
sage: %time MOLS_table(30,1)
...
CPU times: user 10.7 s, sys: 0 ns, total: 10.7 s Wall time: 10.7 s
}}}

After
{{{
sage: %time MOLS_table(30,1)
...
CPU times: user 6.98 s, sys: 4 ms, total: 6.99 s Wall time: 6.99 s
}}}

URL: http://trac.sagemath.org/16875
Reported by: ncohen
Ticket author(s): Vincent Delecroix
Reviewer(s): Nathann Cohen
Trac #16877: Misleading help in sage -i

From sage-devel:
{{{
$ ./sage -i ntl
Package ntl-6.1.0.p0 is already installed.
Use 'sage -f /home/jm58660/sage-6.3/upstream/ntl-6.1.0.tar.bz2' to force
a reinstallation.

$ ./sage -f /home/jm58660/sage-6.3/upstream/ntl-6.1.0.tar.bz2
  . . .
/home/jm58660/sage-6.3/src/bin/sage-spkg: line 601: cd:
ntl-6.1.0.tar.bz2: No such file or directory
}}}

URL: http://trac.sagemath.org/16877
Reported by: vbraun
Ticket author(s): Volker Braun
Reviewer(s): Dima Pasechnik