Drop ancient oseries method
Drop _hashable_content (inherit from Basic)
Change dict.has_key(key) to key in dict
pep8: E211 whitespace before '('
pep8: E703 statement ends with a semicolon
UnXFAIL test_sympy__matrices__expressions__matexpr__ZeroMatrix
Add test for #7231, fixed with pr#2846, fixes #7231
UnXFAIL test_as_coeff_add
Change remaining iteritems to items
Enable code for _EXPAND_INTS=True in cos._eval_rewrite_as_sqrt

See pr #2645 and issue #7210.

The "_EXPAND_INTS" flag allows rewritting cosine (and sin) in cases
where the formula isn't closed over the rationals, e.g.:

    >>> cos(pi/14).rewrite(sqrt)
    sqrt(cos(pi/7)/2 + 1/2)
Removed unused and untested code in polycontext.py, fix #7210 (see also pr #2645)
Merge pull request #7306 from skirpichev/misc

Misc fixes