Bug fixes, optimizations
- [BUGFIX] Fix double-free when emptying a packet number space.
- [BUGFIX] http_server: fix md5sum handler: handle EOF correctly.
- [BUGFIX] Use random values in bits 4 and 5 of the first byte of verneg packets (regression introduced in 2.5.0).
- [OPTIMIZATION] Don't compile in expensive attq checks by default.
- [OPTIMIZATION] http_server: compile regexes only once.