Added checks to ensure provided directory for dump files is valid and correctly formatted, defaults to CWD if not provided
fixed possible crash in case dump thread is canceled and cleanup function is called twice
fixed possible crash in case dump thread is canceled and remove_flow() is called before dump thread actually terminated
fixed that uninit_flow() invalidates all existing pointers to flows following the one in question
Merge pull request #126 from MarcelNehring/squash

Partially fixed tcpdumping (option -M)