src/logging.cc: encapsulate log cleaner, match logfile with <base_filename_><date>-<time>.<pid>

[aesophor]

Previously log cleaner could be broken if users use SetLogDestination() to set a custom base_filename_, as discussed here: #432 (comment)

This PR fixes this bug by checking if a log's filename starts with base_filename_.

[sergiud]

@cswuyg Could you please review the changes?

[aesophor]

@sergiud I've been using this patch in my own projects for a week and it seems to work well. Tested on both Linux and Windows.

[aesophor]

Please don't merge it yet, I've found a potential bug:

Currently I'm checking if a file is a glog's logfile by checking if its filename starts with base_filename_, but this might also delete non-glog logfiles. I should make sure the entire filename matches the format of a glog's filename.

[aesophor]

@sergiud I've revised the patch and re-tested it. LogCleaner::IsLogFromCurrentProject() will now check if the given filename matches the format <base_filename><YYYYMMDD>-<HHMMSS>.<pid>.

[sergiud]

Please resolve the conflict.

[aesophor]

@sergiud I've resolved the conflict. Thanks!