remove unused code
Create a dummy initialize.py which says to run "setup.py initialize"

This is to help users migrating from 0.5
Minor fix for "database not found" warning

Use sys.executable as the python command and avoid using a -1 exit
status
Handle cases where sys.executable is empty or None

The Python docs say "If Python is unable to retrieve the real path to
its executable, sys.executable will be an empty string or None." Fall
back to 'python' if this happens.
Fix IntegerDigits[b^n, b] sometimes being incorrect

To calculate the number of digits in IntegerDigits[x, b], we calculate
log(x)/log(b) in floating-point. The result is machine-specific, and
might be slightly under n if x == b^n, in which case we would return
the wrong answer.

Robustify convert_int_to_digit_list against floating-point inaccuracy
by initially overestimating the number of digits in the result, and
then trimming any unnecessary ones later.