optimise indexing and slicing of bytearray
add assert to find cases where we fail to generate code for indexing/slicing

--HG--
extra : amend_source : b6140bfd07fdf9ae0c7dde2037b3cbff682260e7
disable Py2.6+ bytearray tests in earlier Python versions
avoid useless lookup of unknown encoding (fixes compiler crash)
merge 0.19.x branch into master
Merge pull request #267 from andreasvc/master

No error checking for PyFloat_AS_DOUBLE() as documented
implement (and thus, fix) index assignments to bytearray objects
add note to fused types docs that they are not supported for attributes of extension types
support bytearray as auto encoding string type

--HG--
rename : tests/run/str_ascii_auto_encoding.pyx => tests/run/bytearray_ascii_auto_encoding.pyx
rename : tests/run/str_default_auto_encoding.pyx => tests/run/bytearray_default_auto_encoding.pyx
fix "__qualname__" of names defined as 'global'
support 'global' in Python class body

--HG--
rename : tests/run/ass2global.pyx => tests/run/ass2global.py
fix test in older Py3.x versions, minor cleanups
fix test
add value range check for C level assignments to bytearray indices in order to mimic the safe Python behaviour
clean up some code redundancy
fix copy&paste code in __Pyx_SetItemInt_ByteArray_Generic()
make fast path in Get/SetItemInt() utility functions safe for sizeof(index type) >= sizeof(Py_ssize_t)
replace some redundant utility functions by explicit exceptions
fix C compiler warning in overflow tests
add another straight exception case to macros