RFC: Comprehensive code review and improvements

[Alhkxsj]

Hi PCManFM team,

I've been studying the PCManFM codebase recently and found some areas that could be improved.
Before I start making changes, I'd like to discuss this with you and hear your suggestions.

Issues Found

Security issues:

1. Signal handler exits without cleanup (src/pcmanfm.c:140-141)
2. Socket file in /tmp may have insufficient permissions (src/single-inst.c:343-349)
3. Some places missing NULL checks
4. Possible buffer overflow risks (src/single-inst.c:412, 426-430)

Code quality:

5. Multiple memory leaks
6. Code style is somewhat inconsistent
7. Build system is a bit outdated (still using automake 1.10+)
8. No static analysis tools integrated

Optimization:

9. Performance could be improved (e.g., adding caching, reducing sync operations)
10. Consider removing GTK+ 2 support
11. Some functions are quite long

Questions I'd like to ask

1. Which issues do you think I should start with?
2. Would you prefer smaller PRs or larger ones?
3. Are there any backward compatibility concerns I should be aware of?
4. Should I add test cases?

Things I'd like to help with

• Fix bugs
• Clean up code
• Add tests
• Update documentation

Thank you very much for maintaining this project, I hope I can help!