removed useless code.

bugfix: fixed compilation failures with nginx 1.7.11+ configured with…

… --with-threads.

doc: claimed that we work with nginx 1.7.4.

doc: we work with nginx 1.7.2.

updated docs to reflect recent changes.

valgrind.suppress: removed most of the "possibly leaked" false positi…

…ves.

now we check the ngx_devel_kit dependency at config time and provide …

…a more friendly error message if it is missing.

fixed a typo.

fixed log_debug.

fixed log_debug.