Fix cacheit to cache Add(x,y) and Add(y,x) correctly.

[goodok]

Before this pull request the Add(x,y) and Add(y,x) yield different objects.

It was because the cacheit is called before __new__ method. In turn, the flatten method is calls inside the __new__.

In this pull request we inject the simple flatting procedure to the cacheit wrapper.

Also we allow to set the @cacheit to the '_hashable_content..' function itself and without infinity recursion.
also cache flatten arguments as synonyms in the cache.

Notes:
Only one tests became failure. It is test_heurisch_symbolic_coeffs and marked as XFAIL.

[goodok]

SymPy Bot Summary: All tests have passed.

Test results html report: http://reviews.sympy.org/report/agZzeW1weTNyDAsSBFRhc2sYlewQDA

Interpreter: /usr/bin/python (2.7.2-final-0)
Architecture: Linux (64-bit)
Cache: yes
Test command: setup.py test
master hash: de84ed2
branch hash: 80c6cd4

Automatic review by SymPy Bot.

[goodok]

SymPy Bot Summary: All tests have passed.

Test results html report: http://reviews.sympy.org/report/agZzeW1weTNyDAsSBFRhc2sYwdwQDA

Interpreter: /usr/bin/python (2.7.2-final-0)
Architecture: Linux (64-bit)
Cache: yes
Test command: setup.py test
master hash: de84ed2
branch hash: 171d331

Automatic review by SymPy Bot.

[goodok]

SymPy Bot Summary: There were test failures.

@goodok: Please fix the test failures.

Test results html report: http://reviews.sympy.org/report/agZzeW1weTNyDAsSBFRhc2sYtbIRDA

Interpreter: /usr/bin/python (2.6.6-final-0)
Architecture: Linux (32-bit)
Cache: yes
Test command: setup.py test
master hash: de84ed2
branch hash: 80c6cd4

Automatic review by SymPy Bot.

[goodok]

SymPy Bot Summary: All tests have passed.

Test results html report: http://reviews.sympy.org/report/agZzeW1weTNyDAsSBFRhc2sYl5MRDA

Interpreter: /usr/bin/python (2.7.2-final-0)
Architecture: Linux (64-bit)
Cache: yes
Test command: setup.py test
master hash: de84ed2
branch hash: 12895e5

Automatic review by SymPy Bot.

[goodok]

SymPy Bot Summary: All tests have passed.

Test results html report: http://reviews.sympy.org/report/agZzeW1weTNyDAsSBFRhc2sYrOQQDA

Interpreter: /home/goodok/a/Python-2.5.6/python (2.5.6-final-0)
Architecture: Linux (64-bit)
Cache: yes
Test command: setup.py test
master hash: de84ed2
branch hash: 12895e5

Automatic review by SymPy Bot.

[goodok]

SymPy Bot Summary: All tests have passed.

Test results html report: http://reviews.sympy.org/report/agZzeW1weTNyDAsSBFRhc2sYr-QQDA

Interpreter: /usr/bin/python (2.6.6-final-0)
Architecture: Linux (32-bit)
Cache: yes
Test command: setup.py test
master hash: de84ed2
branch hash: 04f42e2

Automatic review by SymPy Bot.