bugfix: ngx.resp.get_headers(): sometimes we might omit the builtin-headers Content-Type, Content-Length, Connection, and Transfer-Encoding. thanks Jon Keys for the report.
tests: made a test case for ngx.on_abort() more tolerant.
Style: added vim modeline.
Style: use macro instead of magic-number.
use lua_pushliteral for string-literals.
Merge pull request #411 from cubicdaiya/feature/ues_luapushliteral2

use lua_pushliteral for string-literals.
Merge pull request #410 from cubicdaiya/feature/use_macro

Style: use macro instead of magic-number.
Merge pull request #409 from cubicdaiya/feature/vim

Style: added vim modeline.
fixed the build failure introduced in commit 109fd454a.
config: now we also explicitly check the Lua ABI/language version in our feature test for a Lua lib.
bugfix: init_worker_by_lua* would conflict with some other nginx C modules (like ngx_proxy) when their merge_loc_conf callbacks (or alike) produce side-effects in cf->cycle. thanks Ruoshan Huang for the report.