Issue 7117: Replace PyOS_ascii_strtod with PyOS_string_to_double in stropmodule as part of short float repr.

Issue 7117: Replace PyOS_ascii_strtod with PyOS_string_to_double in cPickle as part of short float repr.

complexobject.c.  Also remove length restriction on unicode inputs to
the complex constructor.

floatobject.c.  Also, remove limitation on length of unicode inputs to
float().

integer of type off_t.  Also, don't assume that long long is available.

Reported by Mark D.

Backport pystrtod.c from py3k.

Initial patch by Gregory Smith;  some tweaks added.

Removed unused function PyFloat_AsStringEx. It is unused in floatobject.c, and it's not declared in any .h file.

pieces are being assembled.  To re-enable, define the preprocessor
symbol PY_SHORT_FLOAT_REPR

Add sys.float_repr_style attribute ('short' if short float
repr is in used;  'legacy' otherwise).

 - add double endianness detection to configure script
 - add configure-time check to see whether we can use inline
   assembly to get and set x87 control word in configure script
 - add functions to get and set x87 control word in Python/pymath.c
 - add pyport.h logic to determine whether it's safe to use the
   short float repr or not

Add the Python/dtoa.c file containing the main algorithms;
add corresponding include file and include in Python.h;
include license information for Python/dtoa.c;
add dtoa.c and dtoa.h to Makefile.