Merge of r4231, r4300, r4303, r4304: Configure/build changes and fixes: *) Revamped "configure --help" text. *) FreeBSD 10-current has recently gotten POSIX_FADV_* macros. A fix for the broken build applied. *) AIX 7 defines sys_nerr in errno.h, therefore <errno.h> included in the sys_nerr test. When sys_nerr and _sys_nerr are missed on a particular platform and our euristic for a maximum errno detection applied always print the maximum errno number we reached instead of printing void. This makes possible to build nginx on AIX 7.1. *) Made it possible to build/install from the SVN checkout.