Missing translations for tutorial.ru.po (issue 3526)
Implement next_lexicographic and prev_lexicographic:wq
Don't rely on bool(Relational) in the Piecewise solver.

Fixes issue 2961:
__nonzero__ method of Rel breaks solve of Piecewise functions
http://code.google.com/p/sympy/issues/detail?id=2961
Solution is valid iff Piecewise conditions are satisfied.
fixed whitespaces
Optimized number of permutations of mappings in heurisch()
Reduced the number of permutations of mapping by not generating cases where mapping[-1] != x
While earlier the number of terms or components of a function being permuted were (say) n after these changes they have reduced to n-1, thus improving the time complexity

Optimized number of permutations of mappings in heurisch()

Inorer to reduce the number of permuations of mapping we can remove the unnecessary_tuples that is one of the form (x, x_)
and can append these to the end of all permuted mappings
renamed store_tuple to unnecessary_permutations
Changed integrate_primitive_polynomial from recursive to iterative

Solved the cases such as risch_integrate(log(x)**1001,x)

Earlier

        risch_integrate((log(x)+1)**1001,x)
        RuntimeError: maximum recursion depth exceeded while calling a Python object

Now

        risch_integrate((log(x)+1)**1001,x)
        gives answer within few seconds without any recursion limit getting exceeded
Implemented risch_integrate for trigonometric, inverse trigonometric and hyperbolic functions

Earlier:

        risch_integrate(sin(x),x)
        NotImplementedError

Now:

        risch_integrate(sin(x),x)
        -cos(x)
        integrate(sin(x),x,risch=True)
        -cos(x)

Added flag "rewrite_complex" to prevent calculation of every integral in terms of complex numbers (as we can get better results from other algorithms).
Conversions of trigonometric , inverse trigno , hyperbolic is implemented a s a fall back measure(if no algorithm gives anti-derivative then all the above functions would be converted into exponential or logarithmic components)

changed self.f.rewrite -> self.newf.rewrite
Add a test with a Piecewise result.
Factors() can handle S.Infinity.

Fixes issue 3807: simplify(tan(zoo) + oo) throws an exception
http://code.google.com/p/sympy/issues/detail?id=3807
add pypy tests for travis
Optimized number of permutations of mappings in heurisch()

This PR makes the "unnecesary_permutaion" aesthetically more comprehensive by using list comprehension instead of filter function. It also removes the "enter -> \n" after the starting of the for loop
fixed formatting and added tests
Merge pull request #2059 from shravas/implement_prev_lexicographic

Implement prev_lexicographic and next_lexicographic
pass along flag in xreplace
stylistic changes added to make the code more readable
Merge pull request #1917 from cheatiiit/risch

Implemented risch_integrate for trigonometric, inverse trigonometric and hyperbolic functions
Merge pull request #1906 from cheatiiit/master

Optimized number of permutations of mappings in heurisch()
Merge pull request #1957 from cheatiiit/new1

Changed integrate_primitive_polynomial from recursive to iterative
Merge pull request #2025 from skirpichev/3526-tutorial-russian

Missing translations for tutorial.ru.po (issue 3526)