Keep the symbol map entries unique.

Duplicates are annoying, and we have hacks upstream to prevent them that
cause trouble.
Always add symbols, so we don't leave any behind.
Keep symbols mapped from all loaded modules.

This way the map contains all the symbols used, not just a snapshot.
Read symbols with spaces in their names.

Before it was changing "UNK: hex" and "EXP: hex" into "UNK:" and "EXP:".
Merge pull request #2560 from unknownbrackets/symbol-map

Keep symbol map entries from between modules