bugfix: we might try sending the response header again in ngx.exit() when the header was already sent.
fixed incompatiblities in nginx 1.5.8 which breaks the resolver API in the nginx core.
updated the tests to reflect recent changes in ngx.exit().
feature: allow use of ngx.exit() in the context of header_filter_by_lua*. but in this context ngx.exit() returns immediately.
reindexed test file t/041-header-filter.t.
minor debugging log tweaks.
bugfix: coroutines might incorrectly enter the "dead" state even right after creation with coroutine.create(). thanks James Hurst for the report.
optimize: we no longer clear the lua_State pointers for dead "light threads" such that their coroutine context structs could be reused by other "light threads" and user coroutines.
bugfix: we did not set the shortcut fields in r->headers_in for request headers in our subrequests created by ngx.location.capture*(). thanks Aviram Cohen for the original patch in #318.
tweaked a test case that could fail randomly on slow machines.
doc: documented that the coroutine.* API can be used in init_by_lua since 0.9.2. thanks Ruoshan Huang for the reminder.
reduce compiling warning(avoid halting compiling)
Merge pull request #322 from zh-ang/master

fixed a compilation warning when PCRE is disabled.
change: ngx.decode_base64() now only accepts string arguments.
refactor: avoided the magic error code -3 in ngx_http_lua_ffi_get_ctx_ref.
ngx_http_lua_ffi_set_ctx_ref: return the error code NGX_HTTP_LUA_FFI_NO_REQ_CTX properly.
added (passing) tests for feeding lua numbers to ngx.md5(), ngx.md5_bin(), and ngx.sha1_bin().
added a (passing) test for providing the resulting match table to ngx.re.match().
feature: added the optional 5th argument to ngx.re.match() which is the user-supplied result table for the captures.

This feature gives 12%+ speedup for simple ngx.re.match() calls with 4
submatch captures.
feature: added new pure C API, ngx_http_lua_ffi_max_regex_cache_size, for FFI-based implementations like lua-resty-core.