Polynomial remainder sequences, gcd, and resultant

Documentation on the computation of gcd's and resultant's of
polynomials via remainder sequences, with emphasis on subresultants.
Computing resultant with subresultants

Reordered the loop in the computation of subresultants to include
one more scalar subresultant, namely, the resultant. Another loop
in the resultant function can then be omitted.

Notes:

1. The subresultants and the resultant of the pair `(f,g)` as computed
   are actually those of the pair `(g,f)` if `\deg(f) < \deg(g)`.
   This may have effect on the signs, but that is harmless in general
   when the resultant is only used for eliminating a variable.
   I have not changed this to save some time in the computation.
   Correct signs may be restored afterwards if that is necessary.

2. The resultant of `(f,0)` is zero indicating that `f` and `0` have
   common roots, namely every root of `f`. However, if `f` is a
   non-zero constant, it has no roots. In this case the resultant
   should be different from zero -- in fact one, by convention.
   I have not changed this as it would break the test in
   test_euclidtools.py.
initial implementation of sympy.physics.quantum.pauli, containing the pauli sigma operators and states that they act on
made pauli operators commute with boson operators
fix bug in use of warnings module. improved support for normal ordering expression of products of mix of differetnt types of operators
improved support for simplification of products that includes an identity operator
Fixed bug in handling of non-operator base Pow instances in sympy.physics.quantum.operatorordering
support for indices for Pauli operators the in quantum.pauli module
Added docstring to lambdified functions

If arguments have names, that is used. Otherwise the stack is inspected
to determine if the name can be inferred *with certainty*. If there is
more than one variable pointing to the object, then the name cannot be
determined with certainty, and 'arg_#', where '#' is the number of the
arg is used.
Added args test. Fixed code style error. Fixed missing import bug in unit test.
added a few more tests for pauli module. fixed bug in unit test.
fix white spaces
added newline at end of file
removed trailing white space
added docstrings and docstring tests/examples
Merge branch 'physics.quantum.pauli' of github.com:jrjohansson/sympy into physics.quantum.pauli
added more unit tests for pauli sigma operators
added more unit tests for quantum pauli operators
integrals: An amendment to spde()

The iterative version of spde() currently assumes that the
coefficient  a  of  Dp  were invariant in the loop, in which
case the values of the multiplier  alpha  are powers of  a.
Otherwise the offset  beta  of the solution will be incorrect.

I have added two test cases where  a  is not invariant.
In the general case,  alpha  can be used instead of a power of  a
to construct the correct value of  beta.
Add fixture so py.test can inject variables into function global
namespace.  Fixes failures in test_coordinate_vars