Use standard '_t' fixed-width types instead of rolling our own, where available

[brc0x1]

This PR switches us to use the standard fixed-width integer types (int8_t, uint32_t, etc.) instead of rolling our own (which we were doing because stdint.h / cstdint didn't exist back in 1998). This is mostly an aesthetic change, but it's one less thing to go awry at configure time.

Couple of other minor small tweaks:

• cArchive::Write() takes a const string reference instead of a string by value
• Catch some exceptions by const reference instead of nonconst reference in keyfile.cpp
• Change return type of cErrorQueue::GetNumErrors()