Several miscellaneous code cleanups:
- Removed all mention of BORLAND_C : we don't (and never have, as far as I know) support that compiler.
- All modern C++ compilers support 'long long' for 64-bit integers, so removed the windows #ifdefs
- Replaced all occurrences of INT_MAX/etc with the typesafe std::numeric_limits<> methods
- Replaced a constant 10,000-byte buffer with a properly ECDSA_size'ed vector (and removed a memcpy)