Fix a few minor issues with `make distclean`.

- Only remove the base directory for in-source installs.
- Use full paths to the source directory.
- Update the help message to be more accurate.
Merge pull request #509 from SaberUK/insp20+make-distclean

Fix a few minor issues with `make distclean`.
Fix disabling IPV6_V6ONLY on sockets, issue #511
Fix logfile path on Windows

Fixes issue #510 reported by @JDowny
Fix gnutls (again) on Windows by using gnutls_transport_set_errno()
m_ssl_gnutls Call gnutls_transport_set_errno() on Windows only
Fix an extremely low risk crash bug in m_connectban.
Merge pull request #526 from SaberUK/insp20+connectban-fix

[2.0] Fix an extremely low risk crash bug in m_connectban.
Fix thread handle leak in threadengine_win32
Remove unused variables, avoid copies where possible, check empty() instead of size() == 0
Most of these were detected by cppcheck
Workaround for std::list::size() having linear complexity on some implementations
Fix m_randquote with 0 quotes
Initialize local_count
m_geoip Set cc in OnSetConnectClass to the newly created string if it was NULL
m_httpd_acl Reread config on rehash
m_channames Fix iteration in ValidateChans()

Spotted by @Adam-
m_mysql Fix crash on rehash when the database tags have been changed in the config
Update authors
m_nicklock Fix wrong hook in SetPriority()
Clean up the FileReader class and all of the modules that use it.

- Modules which use this class will now have to catch a
  CoreException when opening files if they wish to ignore
  the failed loading of a file.
- m_randquote has been cleaned up massively and the RANDQUOTE
  command has been removed as it was pretty much useless.