Modified base_string to throw exceptions if construction fails, and to return error conditions if its functions fail (instead of exceptions).
Improved failure detection in base_string functions.
Fixed a couple of problems the meager unit tests we have caught. Fixed up the unit tests a bit.
Added failure checking code to base_integer. Did some refactoring in base.cpp.
Implemented more tests of base_string. Deleted old test file (not being used).